View source for Large numbers

{{short description|Numbers significantly larger than those used regularly}}
{{other uses|Large number (disambiguation)}}
'''Large numbers''' are numbers far larger than those encountered in everyday life, such as simple counting or financial transactions. These quantities appear prominently in [[Mathematics|mathematics]], [[Astronomy:Physical cosmology|cosmology]], [[Cryptography|cryptography]], and [[Physics:Statistical mechanics|statistical mechanics]].  '''Googology''' studies the naming conventions and properties of these immense numbers.<ref>{{Cite book |last1=Darling |first1=David |title=Weird Maths: At the Edge of Infinity and Beyond |last2=Banerjee |first2=Agnijo |date=2018-01-01 |publisher=Harper Collins |isbn=978-93-5277-990-1}}</ref><ref>{{Cite book |last=Nowlan |first=Robert A. |url=https://books.google.com/books?id=Y87bDgAAQBAJ&pg=PA220 |title=Masters of Mathematics: The Problems They Solved, Why These Are Important, and What You Should Know about Them |date=2017-04-09 |publisher=[[Company:Brill Publishers|Brill Publishers]] |isbn=978-94-6300-892-1 |publication-date=2019 |page=220 |chapter=Chapter 14: Large and Small |chapter-url=https://brill.com/display/book/9789463008938/BP000015.xml |chapter-format=PDF}}</ref>

Since the customary [[Decimal|decimal]] format of large numbers can be lengthy, other systems have been devised that allows for shorter representation. For example, a [[Billion|billion]] is represented as 10 characters (1,000,000,000) in decimal format, but is only 3 characters (10<sup>9</sup>) when expressed in [[Exponentiation|exponential format]]. A [[Trillion|trillion]] is 13 characters in decimal, but only four (10<sup>12</sup>) in exponential. Values that vary dramatically can be represented and compared [[Graphics|graphically]] via [[Logarithmic scale|logarithmic scale]].

==Natural language numbering==
{{Main|Names of large numbers}}

A [[Philosophy:Natural language|natural language]] numbering system represents large numbers using names rather than a series of digits. For example "[[Billion|billion]]" may be easier to comprehend for some readers than "1,000,000,000". Sometimes it is shortened by using a suffix, for example 2,340,000,000 = 2.34B (B = billion). A numeric value can be lengthy when expressed in words, for example, "2,345,789" is "two million, three hundred forty five thousand, seven hundred and eighty nine".

==Scientific notation==
[[Scientific notation]] was devised to represent the vast range of values encountered in scientific research in a format that is more compact than traditional formats yet allows for high precision when called for.<ref name=":1">{{Cite book |last=Earl |first=Richard |url=https://doi.org/10.1093/acref/9780198845355.001.0001 |title=The Concise Oxford Dictionary of Mathematics |last2=Nicholson |first2=James |date=2021 |publisher=Oxford University Press |isbn=978-0-19-884535-5}}</ref> A value is represented as a [[Decimal fraction|decimal fraction]] [[Multiplication|times]] a multiple [[Power of 10|power of 10]].<ref name=":1" /> The factor is intended to make reading comprehension easier than a lengthy series of zeros. For example, 1.0{{e|9}} expresses one billion {{Ndash}} 1 followed by nine zeros. The [[Multiplicative inverse|reciprocal]], one billionth, is 1.0{{e|-9}}. Sometimes the letter ''e'' replaces the exponent, for example 1 billion may be expressed as 1e9 instead of 1.0{{e|9}}.

==Examples==
*[[Googol|googol]] = <math>10^{100}</math>
*[[Centillion|centillion]] = <math>10^{303}</math> or <math>10^{600}</math>, depending on the number naming system
*millinillion = <math>10^{3003}</math> or <math>10^{6000}</math>, depending on the number naming system
*The largest known [[Smith number]] = (10<sup>1031</sup>−1) × (10<sup>4594</sup> + 3{{e|2297}} + 1)<sup>1476</sup> {{e|3913210}}
*The largest known [[Mersenne prime]] = <math>2^{136,279,841}-1</math><ref name=":0">{{cite web|title=Mersenne Prime Discovery - 2^136279841 is Prime!|url=https://www.mersenne.org/primes/?press=M136279841|website=Great Internet Mersenne Prime Search}}</ref>
*[[Googolplex|googolplex]] = <math>10^{\text{googol}}=10^{10^{100}}</math>
*[[Skewes's number]]s: the first is approximately <math>10^{10^{10^{34}}}</math>, the second <math>10^{10^{10^{964}}}</math>
*[[Graham's number]], larger than what can be represented even using power towers ([[Tetration|tetration]]). However, it can be represented using layers of [[Knuth's up-arrow notation]].
*[[Kruskal's tree theorem]] is a sequence relating to graphs. TREE(3) is larger than [[Graham's number]].
*[[Rayo's number]] is a large number named after Agustín Rayo which has been claimed to be the largest named number. It was originally defined in a "big number duel" at [[Organization:Massachusetts Institute of Technology|MIT]] on 26 January 2007.
Examples of large numbers describing real-world things:

* The number of [[Cell|cells]] in the human body (estimated at 3.72{{e|13}}), or 37.2 trillion<ref>{{Cite journal|last1=Bianconi|first1=Eva|last2=Piovesan|first2=Allison|last3=Facchin|first3=Federica|last4=Beraudi|first4=Alina|last5=Casadei|first5=Raffaella|last6=Frabetti|first6=Flavia|last7=Vitale|first7=Lorenza|last8=Pelleri|first8=Maria Chiara|last9=Tassani|first9=Simone|date=Nov–Dec 2013|title=An estimation of the number of cells in the human body|journal=Annals of Human Biology|volume=40|issue=6|pages=463–471|doi=10.3109/03014460.2013.807878|issn=1464-5033|pmid=23829164|hdl=11585/152451 |s2cid=16247166|doi-access=free}}</ref>
* The number of [[Bit|bit]]s on a computer hard disk ({{as of|2024|lc=true}}, typically about 10<sup>13</sup>, 1–2&nbsp;[[Terabyte|TB]]), or 10 trillion<!-- If you think this is wrong, read the numbers again, carefully. These are bits, not bytes. -->
* The number of [[Software:Neuron|neuronal connections]] in the human brain (estimated at 10<sup>14</sup>), or 100 trillion
* The [[Physics:Avogadro constant|Avogadro constant]] is the number of "elementary entities" (usually atoms or molecules) in one [[Mole (unit)|mole]]; the number of atoms in 12&nbsp;grams of [[Physics:Carbon-12|carbon-12]]{{Snd}} approximately {{val|6.022|e=23}}, or 602.2 sextillion.
* The total number of [[Biology:DNA|DNA]] [[Biology:Base pair|base pair]]s within the entire [[Earth:Biomass (ecology)|biomass]] on Earth, as a possible approximation of global [[Biology:Biodiversity|biodiversity]], is estimated at {{val|5.3|3.6|e=37}}, or 53±36 undecillion<ref>{{cite journal | vauthors = Landenmark HK, Forgan DH, Cockell CS | title = An Estimate of the Total DNA in the Biosphere | journal = PLOS Biology | volume = 13 | issue = 6 | article-number = e1002168 | date = June 2015 | pmid = 26066900 | pmc = 4466264 | doi = 10.1371/journal.pbio.1002168 | doi-access = free }}</ref><ref name="NYT-20150718-rn">{{cite news |last=Nuwer |first=Rachel |  name-list-style = vanc |date=18 July 2015 |title=Counting All the DNA on Earth |url=https://www.nytimes.com/2015/07/21/science/counting-all-the-dna-on-earth.html |work=The New York Times |location=New York |issn=0362-4331 |access-date=2015-07-18}}</ref><!--- PLOS paper cited by NYT used 'tonne' unit. --->
* The Earth consists of about 4 × 10<sup>51</sup>, or 4 sexdecillion, [[Physics:Nucleon|nucleon]]s
* The estimated number of [[Atom|atom]]s in the [[Astronomy:Observable universe|observable universe]] (10<sup>80</sup>), or 100 quinvigintillion
* The lower bound on the game-tree complexity of chess, also known as the "[[Shannon number]]" (estimated at 10<sup>120</sup>), or 1 novemtrigintillion.<ref>{{cite journal | author = Shannon, Claude | title = XXII. Programming a Computer for Playing Chess | journal = Philosophical Magazine | series = Series 7 | volume = 41 | issue = 314 | date = March 1950 | url = http://archive.computerhistory.org/projects/chess/related_materials/text/2-0%20and%202-1.Programming_a_computer_for_playing_chess.shannon/2-0%20and%202-1.Programming_a_computer_for_playing_chess.shannon.062303002.pdf |  access-date = 2019-01-25 | archive-url = https://web.archive.org/web/20100706211229/http://archive.computerhistory.org/projects/chess/related_materials/text/2-0%20and%202-1.Programming_a_computer_for_playing_chess.shannon/2-0%20and%202-1.Programming_a_computer_for_playing_chess.shannon.062303002.pdf | archive-date = 2010-07-06 }}</ref> Note that this value of the Shannon number is for Standard Chess. It has even larger values for larger-board chess variants such as Grant Acedrex, Tai Shogi, and Taikyoku Shogi.

== Astronomical ==
In [[Astronomy:Astronomy|astronomy]] and [[Philosophy:Cosmology|cosmology]] large numbers for measures of length and time are encountered. For instance, according to the prevailing Big Bang model, the universe is approximately 13.8 billion years old (equivalent to {{val|4.355|e=17}} seconds). The [[Astronomy:Observable universe|observable universe]] spans 93 billion [[Light-year|light years]] (approximately {{val|8.8|e=26}} meters) and hosts around {{val|5|e=22}} stars, organized into roughly 125 billion galaxies (as observed by the Hubble Space Telescope). As a rough estimate, there are about {{val|e=80}} atoms within the observable universe.<ref>[http://www.universetoday.com/36302/atoms-in-the-universe/#gsc.tab=0 Atoms in the Universe]. Universe Today. 30-07-2009. Retrieved 02-03-13.</ref>

According to Don Page, physicist at the University of Alberta, Canada, the longest finite time that has so far been explicitly calculated by any physicist is

::::<math>10^{10^{10^{10^{10^{1.1}}}}} \mbox{ years}</math>

(which corresponds to the scale of an estimated [[Poincaré recurrence theorem|Poincaré recurrence time]] for the quantum state of a hypothetical box containing a black hole with the estimated mass of the entire universe, observable or not, assuming a certain [[Astronomy:Inflation (cosmology)|inflationary]] model with an [[Astronomy:Inflaton|inflaton]] whose mass is 10<sup>−6</sup> [[Physics:Planck mass|Planck mass]]es), roughly   10^10^1.288*10^3.884 T  <ref name=page95>Information Loss in Black Holes and/or Conscious Beings?, Don N. Page, ''Heat Kernel Techniques and Quantum Gravity'' (1995), S. A. Fulling (ed), p. 461. Discourses in Mathematics and its Applications, No. 4, Texas A&M University Department of Mathematics. {{arxiv|hep-th/9411193}}. {{isbn|0-9630728-3-8}}.</ref><ref>[http://www.fpx.de/fp/Fun/Googolplex/GetAGoogol.html How to Get A Googolplex]</ref> This time assumes a statistical model subject to Poincaré recurrence. A much simplified way of thinking about this time is in a model where the universe's history [[Physics:Loschmidt's paradox|repeats itself]] arbitrarily many times due to [[Ergodic hypothesis|properties of statistical mechanics]]; this is the time scale when it will first be somewhat similar (for a reasonable choice of "similar") to its current state again.

Combinatorial processes give rise to astonishingly large numbers. The  [[Factorial|factorial]] function, which quantifies [[Permutation|permutation]]s of a fixed set of objects, grows superexponentially as the number of objects increases.  [[Stirling's formula]] provides a precise asymptotic expression for this rapid growth.

In statistical mechanics, combinatorial numbers reach such immense magnitudes that they are often expressed using [[Logarithm|logarithm]]s.

Gödel numbers, along with similar representations of bit-strings in [[Algorithmic information theory|algorithmic information theory]], are vast—even for mathematical statements of moderate length. Remarkably, certain [[Pathological (mathematics)|pathological]] numbers surpass even the Gödel numbers associated with typical mathematical propositions.

Logician Harvey Friedman has made significant contributions to the study of very large numbers, including work related to [[Kruskal's tree theorem]] and the [[Robertson–Seymour theorem]].

==="Millions and billions"===
To help viewers of ''Cosmos'' distinguish between "millions" and "billions", astronomer [[Biography:Carl Sagan|Carl Sagan]] stressed the "b". Sagan never did, however, say "billions and billions". The public's association of the phrase and Sagan came from a ''Tonight Show'' skit. Parodying Sagan's effect, Johnny Carson quipped "billions and billions".<ref>[http://www.csicop.org/si/show/carl_sagan_takes_questions Carl Sagan takes questions more from his 'Wonder and Skepticism' CSICOP 1994 keynote, Skeptical Inquirer] {{webarchive |url=https://web.archive.org/web/20161221054208/http://www.csicop.org/si/show/carl_sagan_takes_questions |date=December 21, 2016 }}</ref> The phrase has, however, now become a humorous fictitious number—the [[Indefinite and fictitious numbers#Sagan's number|Sagan]].  ''Cf.'', [[Biography:Carl Sagan#Sagan units|Sagan Unit]].

== Standardized system of writing ==
{{Very long section|date=January 2026}}
A standardized way of writing very large numbers allows them to be easily sorted in increasing order, and one can get a good idea of how much larger a number is than another one.

To compare numbers in scientific notation, say 5×10<sup>4</sup> and 2×10<sup>5</sup>, compare the exponents first, in this case 5 > 4, so 2×10<sup>5</sup> > 5×10<sup>4</sup>. If the exponents are equal, the mantissa (or coefficient) should be compared, thus 5×10<sup>4</sup> > 2×10<sup>4</sup> because 5 > 2.

Tetration with base 10 gives the sequence <math>10 \uparrow \uparrow n=10 \to n \to 2=(10\uparrow)^n 1</math>, the power towers of numbers 10, where <math>(10\uparrow)^n</math> denotes a functional power of the function <math>f(n)=10^n</math> (the function also expressed by the suffix "-plex" as in googolplex, see [[Names of large numbers#The googol family|the googol family]]).

These are very round numbers, each representing an [[Order of magnitude|order of magnitude]] in a generalized sense. A crude way of specifying how large a number is, is specifying between which two numbers in this sequence it is.

More precisely, numbers in between can be expressed in the form <math>(10\uparrow)^n a</math>, i.e., with a power tower of 10s, and a number at the top, possibly in scientific notation, e.g. <math>10^{10^{10^{10^{10^{4.829}}}}} = (10\uparrow)^5 4.829</math>, a number between <math>10\uparrow\uparrow 5</math> and <math>10\uparrow\uparrow 6</math> (note that <math>10 \uparrow\uparrow n < (10\uparrow)^n a < 10 \uparrow\uparrow (n+1)</math> if <math> 1 < a < 10</math>). (See also [[Tetration#Extension to real heights|extension of tetration to real heights]].)

Thus googolplex is <math>10^{10^{100}} = (10\uparrow)^2 100 = (10\uparrow)^3 2</math>.

Another example:
:<math>2 \uparrow\uparrow\uparrow 4 = 
  \begin{matrix}
   \underbrace{2_{}^{2^{{}^{.\,^{.\,^{.\,^2}}}}}}\\
   \qquad\quad\ \ \ 65,536\mbox{ copies of }2  \end{matrix}
  \approx (10\uparrow)^{65,531}(6 \times 10^{19,728}) \approx (10\uparrow)^{65,533} 4.3
</math> (between <math>10\uparrow\uparrow 65,533</math> and <math>10\uparrow\uparrow 65,534</math>)

Thus the "order of magnitude" of a number (on a larger scale than usually meant), can be characterized by the number of times (''n'') one has to take the <math>log_{10}</math> to get a number between 1 and 10. Thus, the number is between <math>10\uparrow\uparrow n</math> and <math>10\uparrow\uparrow (n+1)</math>. As explained, a more precise description of a number also specifies the value of this number between 1 and 10, or the previous number (taking the logarithm one time less) between 10 and 10<sup>10</sup>, or the next, between 0 and 1.

Note that
:<math>10^{(10\uparrow)^{n}x}=(10\uparrow)^{n}10^x</math>
I.e., if a number ''x'' is too large for a representation <math>(10\uparrow)^{n}x</math> the power tower can be made one higher, replacing ''x'' by log<sub>10</sub>''x'', or find ''x'' from the lower-tower representation of the log<sub>10</sub> of the whole number. If the power tower would contain one or more numbers different from 10, the two approaches would lead to different results, corresponding to the fact that extending the power tower with a 10 at the bottom is then not the same as extending it with a 10 at the top (but, of course, similar remarks apply if the whole power tower consists of copies of the same number, different from 10).

If the height of the tower is large, the various representations for large numbers can be applied to the height itself. If the height is given only approximately,  giving a value at the top does not make sense, so the double-arrow notation (e.g. <math>10\uparrow\uparrow(7.21\times 10^8)</math>) can be used. If the value after the double arrow is a very large number itself, the above can recursively be applied to that value.

Examples:
:<math>10\uparrow\uparrow 10^{\,\!10^{10^{3.81\times 10^{17}}}}</math> (between <math>10\uparrow\uparrow\uparrow 2</math> and <math>10\uparrow\uparrow\uparrow 3</math>)
:<math>10\uparrow\uparrow 10\uparrow\uparrow (10\uparrow)^{497}(9.73\times 10^{32})=(10\uparrow\uparrow)^{2} (10\uparrow)^{497}(9.73\times 10^{32})</math> (between <math>10\uparrow\uparrow\uparrow 4</math> and <math>10\uparrow\uparrow\uparrow 5</math>)

Similarly to the above, if the exponent of <math>(10\uparrow)</math> is not exactly given then giving a value at the right does not make sense, and instead of using the power notation of <math>(10\uparrow)</math>, it is possible to add <math>1</math> to the exponent of <math>(10\uparrow\uparrow)</math>, to obtain e.g. <math>(10\uparrow\uparrow)^{3} (2.8\times 10^{12})</math>.

If the exponent of <math>(10\uparrow \uparrow)</math> is large, the various representations for large numbers can be applied to this exponent itself. If this exponent is not exactly given then, again, giving a value at the right does not make sense, and instead of using the power notation of <math>(10\uparrow \uparrow)</math> it is possible use the triple arrow operator, e.g. <math>10\uparrow\uparrow\uparrow(7.3\times 10^{6})</math>.

If the right-hand argument of the triple arrow operator is large the above applies to it, obtaining e.g. <math>10\uparrow\uparrow\uparrow(10\uparrow\uparrow)^{2} (10\uparrow)^{497}(9.73\times 10^{32})</math> (between <math>10\uparrow\uparrow\uparrow 10\uparrow\uparrow\uparrow 4</math> and <math>10\uparrow\uparrow\uparrow 10\uparrow\uparrow\uparrow 5</math>). This can be done recursively, so it is possible to have a power of the triple arrow operator.

Then it is possible to proceed with operators with higher numbers of arrows, written <math>\uparrow^n</math>.

Compare this notation with the hyper operator and the [[Conway chained arrow notation]]:
:<math>a\uparrow^n b</math> = ( ''a'' → ''b'' → ''n'' ) = hyper(''a'',&nbsp;''n''&nbsp;+&nbsp;2,&nbsp;''b'')
An advantage of the first is that when considered as function of ''b'', there is a natural notation for powers of this function (just like when writing out the ''n'' arrows): <math>(a\uparrow^n)^k b</math>. For example:

:<math>(10\uparrow^2)^3 b</math> = ( 10 → ( 10 → ( 10 → ''b'' → 2 ) → 2 ) → 2 )
and only in special cases the long nested chain notation is reduced; for <math>''b'' = 1</math> obtains:
:<math>10\uparrow^3 3 = (10\uparrow^2)^3 1</math> = ( 10 → 3 → 3 )

Since the ''b'' can also be very large, in general it can be written instead a number with a sequence of powers <math>(10 \uparrow^n)^{k_n}</math> with decreasing values of ''n'' (with exactly given integer exponents <math>{k_n}</math>) with at the end a number in ordinary scientific notation. Whenever a <math>{k_n}</math> is too large to be given exactly, the value of <math>{k_{n+1}}</math> is increased by 1 and everything to the right of <math>({n+1})^{k_{n+1}}</math> is rewritten.

For describing numbers approximately, deviations from the decreasing order of values of ''n'' are not needed. For example, <math>10 \uparrow (10 \uparrow \uparrow)^5 a=(10 \uparrow \uparrow)^6 a</math>, and <math>10 \uparrow (10 \uparrow \uparrow \uparrow 3)=10 \uparrow \uparrow (10 \uparrow \uparrow 10 + 1)\approx 10 \uparrow \uparrow \uparrow 3</math>. Thus is obtained the somewhat counterintuitive result that a number ''x'' can be so large that, in a way, ''x'' and 10<sup>x</sup> are "almost equal" (for arithmetic of large numbers see also below).

If the superscript of the upward arrow is large, the various representations for large numbers can be applied to this superscript itself. If this superscript is not exactly given then there is no point in raising the operator to a particular power or to adjust the value on which it act, instead it is possible to simply use a standard value at the right, say 10, and the expression reduces to <math>10 \uparrow^n 10=(10 \to 10 \to n)</math> with an approximate ''n''. For such numbers the advantage of using the upward arrow notation no longer applies, so the chain notation can be used instead.

The above can be applied recursively for this ''n'', so the notation <math>\uparrow^n</math> is obtained in the superscript of the first arrow, etc., or a nested chain notation, e.g.:

:(10 → 10 → (10 → 10 → <math>3 \times 10^5</math>) ) = <math>10 \uparrow ^{10 \uparrow ^{3 \times 10^5} 10} 10 </math>

If the number of levels gets too large to be convenient, a notation is used where this number of levels is written down as a number (like using the superscript of the arrow instead of writing many arrows). Introducing a function <math>f(n)=10 \uparrow^{n} 10</math> = (10 → 10 → ''n''), these levels become functional powers of ''f'', allowing us to write a number in the form <math>f^m(n)</math> where ''m'' is given exactly and n is an integer which may or may not be given exactly (for example: <math>f^2(3 \times 10^5)</math>). If ''n'' is large, any of the above can be used for expressing it. The "roundest" of these numbers are those of the form ''f''<sup>''m''</sup>(1) = (10→10→''m''→2). For example, <math>(10 \to 10 \to 3\to 2) = 10 \uparrow ^{10 \uparrow ^{10^{10}} 10} 10 </math>

Compare the definition of Graham's number: it uses numbers 3 instead of 10 and has 64 arrow levels and the number 4 at the top; thus <math> G < 3\rightarrow 3\rightarrow 65\rightarrow 2 <(10 \to 10 \to 65\to 2)=f^{65}(1)</math>, but also <math> G < f^{64}(4)<f^{65}(1)</math>.

If ''m'' in <math>f^m(n)</math> is too large to give exactly, it is possible to use a fixed ''n'', e.g. ''n'' = 1, and apply the above recursively to ''m'', i.e., the number of levels of upward arrows is itself represented in the superscripted upward-arrow notation, etc. Using the functional power notation of ''f'' this gives multiple levels of ''f''. Introducing a function <math>g(n)=f^{n}(1)</math> these levels become functional powers of ''g'', allowing us to write a number in the form <math>g^m(n)</math> where ''m'' is given exactly and n is an integer which may or may not be given exactly. For example, if (10→10→''m''→3) = ''g''<sup>''m''</sup>(1). If ''n'' is large any of the above can be used for expressing it. Similarly a function ''h'', etc. can be introduced. If many such functions are required, they can be numbered instead of using a new letter every time, e.g. as a subscript, such that there are numbers of the form <math>f_k^m(n)</math> where ''k'' and ''m'' are given exactly and n is an integer which may or may not be given exactly. Using ''k''=1 for the ''f'' above, ''k''=2 for ''g'', etc., obtains (10→10→''n''→''k'') = <math>f_k(n)=f_{k-1}^n(1)</math>. If ''n'' is large any of the above can be used to express it. Thus is obtained a nesting of forms <math>{f_k}^{m_k}</math> where going inward the ''k'' decreases, and with as inner argument a sequence of powers <math>(10 \uparrow^n)^{p_n}</math> with decreasing values of ''n'' (where all these numbers are exactly given integers) with at the end a number in ordinary scientific notation.

When ''k'' is too large to be given exactly, the number concerned can be expressed as <math>{f_n}(10)</math>=(10→10→10→''n'') with an approximate ''n''. Note that the process of going from the sequence <math>10^{n}</math>=(10→''n'') to the sequence <math>10 \uparrow^n 10</math>=(10→10→''n'') is very similar to going from the latter to the sequence <math>{f_n}(10)</math>=(10→10→10→''n''): it is the general process of adding an element 10 to the chain in the chain notation; this process can be repeated again (see also the previous section). Numbering the subsequent versions of this function a number can be described using functions <math>{f_{qk}}^{m_{qk}}</math>, nested in [[Lexicographical order|lexicographical order]] with ''q'' the most significant number, but with decreasing order for ''q'' and for ''k''; as inner argument yields a sequence of powers <math>(10 \uparrow^n)^{p_n}</math> with decreasing values of ''n'' (where all these numbers are exactly given integers) with at the end a number in ordinary scientific notation.

For a number too large to write down in the Conway chained arrow notation it size can be described by the length of that chain, for example only using elements 10 in the chain; in other words, one could specify its position in the sequence 10, 10→10, 10→10→10, .. If even the position in the sequence is a large number same techniques can be applied again.

===Examples===
Numbers expressible in decimal notation:
*2<sup>2</sup> = 4
*2<sup>2<sup>2</sup></sup> = 2 ↑↑ 3 = 16
*3<sup>3</sup> = 27
*4<sup>4</sup> = 256
*5<sup>5</sup> = 3,125
*6<sup>6</sup> = 46,656
*<math>2^{2^{2^{2}}}</math> = 2 ↑↑ 4 = 2↑↑↑3 = 65,536
*7<sup>7</sup> = 823,543
*10<sup>6</sup> = 1,000,000 = 1 million
*8<sup>8</sup> = 16,777,216
*9<sup>9</sup> = 387,420,489
*10<sup>9</sup> = 1,000,000,000 = 1&nbsp;billion
*10<sup>10</sup> = 10,000,000,000
*10<sup>12</sup> = 1,000,000,000,000 = 1&nbsp;trillion
*3<sup>3<sup>3</sup></sup> = 3 ↑↑ 3 =  7,625,597,484,987 ≈ 7.63 × 10<sup>12</sup>
*10<sup>15</sup> = 1,000,000,000,000,000 = 1&nbsp;million billion = 1 quadrillion
*10<sup>18</sup> = 1,000,000,000,000,000,000 = 1&nbsp;billion billion = 1 quintilion
Numbers expressible in scientific notation:
*Approximate [[Astronomy:Observable universe#Matter content—number of atoms|number of atoms in the observable universe]] = 10<sup>80</sup> = 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
*googol = 10<sup>100</sup> = 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000<ref>{{Cite news |last=Journal Online |first=Carl BialikThe Wall Street |date=2004-06-14 |title=There Could Be No Google Without Edward Kasner |url=https://www.wsj.com/articles/SB108575924921724042 |access-date=2025-06-18 |work=Wall Street Journal |language=en-US |issn=0099-9660}}</ref>
*4<sup>4<sup>4</sup></sup> = 4 ↑↑ 3 = 2<sup>512</sup> ≈ 1.34 × 10<sup>154</sup> ≈ (10 ↑)<sup>2</sup> 2.2
*Approximate number of [[Physics:Planck length|Planck volumes]] composing the volume of the observable [[Universe|universe]] = 8.5 × 10<sup>184</sup>
*5<sup>5<sup>5</sup></sup> = 5 ↑↑ 3 = 5<sup>3125</sup> ≈ 1.91 × 10<sup>2184</sup> ≈ (10 ↑)<sup>2</sup> 3.3
*<math>2^{2^{2^{2^2}}} = 2 \uparrow \uparrow 5 = 2^{65,536} \approx 2.0 \times 10^{19,728} \approx (10 \uparrow)^2 4.3</math>
*6<sup>6<sup>6</sup></sup> = 6 ↑↑ 3 ≈ 2.66 × 10<sup>36,305</sup> ≈ (10 ↑)<sup>2</sup> 4.6
*7<sup>7<sup>7</sup></sup> = 7 ↑↑ 3 ≈ 3.76 × 10<sup>695,974</sup> ≈ (10 ↑)<sup>2</sup> 5.8
*8<sup>8<sup>8</sup></sup> = 8 ↑↑ 3 ≈ 6.01 × 10<sup>15,151,335</sup> ≈ (10 ↑)<sup>2</sup> 7.2
*<math>M_{136,279,841} \approx 8.82\times 10^{41,024,319} \approx 10^{10^{7.6130}} \approx (10 \uparrow)^2 \ 7.6130</math>, the 52nd and {{As of|2024|10|lc=y}} the largest known [[Mersenne prime]].<ref name=":0" />
*9<sup>9<sup>9</sup></sup> = 9 ↑↑ 3 ≈ 4.28 × 10<sup>369,693,099</sup> ≈ (10 ↑)<sup>2</sup> 8.6
*10<sup>10<sup>10</sup></sup> =10 ↑↑ 3 = 10<sup>10,000,000,000</sup> = (10 ↑)<sup>3</sup> 1
*<math>3^{3^{3^{3}}} = 3 \uparrow \uparrow 4 \approx 1.26 \times 10^{3,638,334,640,024} \approx (10 \uparrow)^3 1.10</math>

Numbers expressible in (10 ↑)<sup>''n''</sup> ''k'' notation:
*googolplex = <math>10^{10^{100}} = (10 \uparrow)^3 2</math>
*<math>2^{2^{2^{2^{2^2}}}} = 2 \uparrow \uparrow 6 = 2^{2^{65,536}} \approx 2^{(10 \uparrow)^2 4.3} \approx 10^{(10 \uparrow)^2 4.3} = (10 \uparrow)^3 4.3</math>
*<math>10^{10^{10^{10}}}=10 \uparrow \uparrow 4=(10 \uparrow)^4 1</math>
*<math>3^{3^{3^{3^3}}} = 3 \uparrow \uparrow 5 \approx 3^{10^{3.6 \times 10^{12}}} \approx (10 \uparrow)^4 1.10</math>
*<math>2^{2^{2^{2^{2^{2^2}}}}} = 2 \uparrow \uparrow 7 \approx (10 \uparrow)^4 4.3</math>
*10 ↑↑ 5 = (10 ↑)<sup>5</sup> 1
*3 ↑↑ 6 ≈ (10 ↑)<sup>5</sup> 1.10
*2 ↑↑ 8 ≈ (10 ↑)<sup>5</sup> 4.3
*10 ↑↑ 6 = (10 ↑)<sup>6</sup> 1
*10 ↑↑↑ 2 = 10 ↑↑ 10 = (10 ↑)<sup>10</sup> 1
*2 ↑↑↑↑ 3 = 2 ↑↑↑ 4 = 2 ↑↑ 65,536 ≈ (10 ↑)<sup>65,533</sup> 4.3 is between 10 ↑↑ 65,533 and 10 ↑↑ 65,534

Bigger numbers:
*3 ↑↑↑ 3 = 3 ↑↑ (3 ↑↑ 3) ≈ 3 ↑↑ 7.6 × 10<sup>12</sup> ≈ 10 ↑↑ 7.6 × 10<sup>12</sup> is between (10 ↑↑)<sup>2</sup> 2 and (10 ↑↑)<sup>2</sup> 3
*<math>10\uparrow\uparrow\uparrow 3=(10 \uparrow \uparrow)^3 1</math> = ( 10 → 3 → 3 )
*<math>(10\uparrow\uparrow)^2 11</math>
*<math>(10\uparrow\uparrow)^2 10^{\,\!10^{10^{3.81\times 10^{17}}}}</math>
*<math>10\uparrow\uparrow\uparrow 4=(10 \uparrow \uparrow)^4 1</math> = ( 10 → 4 → 3 )
*<math>(10\uparrow\uparrow)^{2} (10\uparrow)^{497}(9.73\times 10^{32})</math>
*<math>10\uparrow\uparrow\uparrow 5=(10 \uparrow \uparrow)^5 1</math> = ( 10 → 5 → 3 )
*<math>10\uparrow\uparrow\uparrow 6=(10 \uparrow \uparrow)^6 1</math> = ( 10 → 6 → 3 )
*<math>10\uparrow\uparrow\uparrow 7=(10 \uparrow \uparrow)^7 1</math> = ( 10 → 7 → 3 )
*<math>10\uparrow\uparrow\uparrow 8=(10 \uparrow \uparrow)^8 1</math> = ( 10 → 8 → 3 )
*<math>10\uparrow\uparrow\uparrow 9=(10 \uparrow \uparrow)^9 1</math> = ( 10 → 9 → 3 )
*<math>10 \uparrow \uparrow \uparrow \uparrow 2 = 10\uparrow\uparrow\uparrow 10=(10 \uparrow \uparrow)^{10} 1</math> = ( 10 → 2 → 4 ) = ( 10 → 10 → 3 )
*The first term in the definition of Graham's number, ''g''<sub>1</sub> = 3 ↑↑↑↑ 3 = 3 ↑↑↑ (3 ↑↑↑ 3) ≈ 3 ↑↑↑ (10 ↑↑ 7.6 × 10<sup>12</sup>) ≈ 10 ↑↑↑ (10 ↑↑ 7.6 × 10<sup>12</sup>) is between (10 ↑↑↑)<sup>2</sup> 2 and (10 ↑↑↑)<sup>2</sup> 3 (See [[Graham's number]])
*<math>10\uparrow\uparrow\uparrow\uparrow 3=(10 \uparrow \uparrow\uparrow)^3 1</math> = (10 → 3 → 4)
*<math>4 \uparrow \uparrow \uparrow \uparrow 4</math> = ( 4 → 4 → 4 ) <math>\approx (10 \uparrow \uparrow \uparrow)^2 (10 \uparrow \uparrow)^3 154</math>
*<math>10\uparrow\uparrow\uparrow\uparrow 4=(10 \uparrow \uparrow\uparrow)^4 1</math> = ( 10 → 4 → 4 )
*<math>10\uparrow\uparrow\uparrow\uparrow 5=(10 \uparrow \uparrow\uparrow)^5 1</math> = ( 10 → 5 → 4 )
*<math>10\uparrow\uparrow\uparrow\uparrow 6=(10 \uparrow \uparrow\uparrow)^6 1</math> = ( 10 → 6 → 4 )
*<math>10\uparrow\uparrow\uparrow\uparrow 7=(10 \uparrow \uparrow\uparrow)^7 1=</math> = ( 10 → 7 → 4 )
*<math>10\uparrow\uparrow\uparrow\uparrow 8=(10 \uparrow \uparrow\uparrow)^8 1=</math> = ( 10 → 8 → 4 )
*<math>10\uparrow\uparrow\uparrow\uparrow 9=(10 \uparrow \uparrow\uparrow)^9 1=</math> = ( 10 → 9 → 4 )
*<math>10 \uparrow \uparrow \uparrow \uparrow \uparrow 2 = 10\uparrow\uparrow\uparrow\uparrow 10=(10 \uparrow \uparrow\uparrow)^{10} 1</math> = ( 10 → 2 → 5 ) = ( 10 → 10 → 4 )
*( 2 → 3 → 2 → 2 ) = ( 2 → 3 → 8 )
*( 3 → 2 → 2 → 2 ) = ( 3 → 2 → 9 ) = ( 3 → 3 → 8 )
*( 10 → 10 → 10 ) = ( 10 → 2 → 11 )
*( 10 → 2 → 2 → 2 ) = ( 10 → 2 → 100 )
*( 10 → 10 → 2 → 2 ) = ( 10 → 2 → <math>10^{10}</math> ) = <math>10 \uparrow ^{10^{10}} 10 </math>
*The second term in the definition of Graham's number, ''g''<sub>2</sub> = 3  ↑<sup>''g''<sub>1</sub></sup> 3 > 10 ↑<sup>''g''<sub>1</sub> – 1</sup> 10.
*( 10 → 10 → 3 → 2 ) = (10 → 10 → (10 → 10 → <math>10^{10}</math>) ) = <math>10 \uparrow ^{10 \uparrow ^{10^{10}} 10} 10 </math>
*''g''<sub>3</sub> = (3  → 3 → ''g''<sub>2</sub>) > (10 → 10 → ''g''<sub>2</sub> – 1) > (10 → 10 → 3 → 2)
*''g''<sub>4</sub> = (3  → 3 → ''g''<sub>3</sub>) > (10 → 10 → ''g''<sub>3</sub> – 1) > (10 → 10 → 4 → 2)
*...
*''g''<sub>9</sub> = (3  → 3 → ''g''<sub>8</sub>) is between (10 → 10 → 9 → 2) and (10 → 10 → 10 → 2)
*( 10 → 10 → 10 → 2 )
*''g''<sub>10</sub> = (3  → 3 → ''g''<sub>9</sub>) is between (10 → 10 → 10 → 2) and (10 → 10 → 11 → 2)
*...
*''g''<sub>63</sub> = (3  → 3 → ''g''<sub>62</sub>) is between (10 → 10 → 63 → 2) and (10 → 10 → 64 → 2)
*( 10 → 10 → 64 → 2 )
*Graham's number, ''g''<sub>64</sub><ref>Regarding the comparison with the previous value: <math>10\uparrow ^n 10 < 3 \uparrow ^{n+1} 3</math>, so starting the 64 steps with 1 instead of 4 more than compensates for replacing the numbers 3 by 10</ref>
*( 10 → 10 → 65 → 2 )
*( 10 → 10 → 10 → 3 )
*( 10 → 10 → 10 → 4 )
*( 10 → 10 → 10 → 10 )
*( 10 → 10 → 10 → 10 → 10 )
*( 10 → 10 → 10 → 10 → 10 → 10 )
*( 10 → 10 → 10 → 10 → 10 → 10 → 10 → ... → 10 → 10 → 10 → 10 → 10 → 10 → 10 → 10 ) where there are ( 10 → 10 → 10 ) "10"s

=== Other notations ===
Some notations for extremely large numbers:
*[[Knuth's up-arrow notation]], hyperoperators, [[Ackermann function]], including tetration
*[[Conway chained arrow notation]]
*Steinhaus-Moser notation; apart from the method of construction of large numbers, this also involves a graphical notation with [[Polygon|polygon]]s. Alternative notations, like a more conventional function notation, can also be used with the same functions.
*[[Fast-growing hierarchy]]

These notations are essentially functions of integer variables, which increase very rapidly with those integers. Ever-faster-increasing functions can easily be constructed recursively by applying these functions with large integers as argument.

A function with a vertical asymptote is not helpful in defining a very large number, although the function increases very rapidly: one has to define an argument very close to the asymptote, i.e. use a very small number, and constructing that is equivalent to constructing a very large number, e.g. the reciprocal.

== Comparison of base values ==
The following illustrates the effect of a base different from 10, base 100. It also illustrates representations of numbers and the arithmetic.

<math>100^{12}=10^{24}</math>, with base 10 the exponent is doubled.

<math>100^{100^{12}}=10^{2*10^{24}}</math>, ditto.

<math>100^{100^{100^{12}}} \approx 10^{10^{2*10^{24}+0.30103}}</math>, the highest exponent is very little more than doubled (increased by log<sub>10</sub>2).

*<math>100\uparrow\uparrow 2=10^ {200} </math>
*<math>100\uparrow\uparrow 3=10^ {2 \times 10^ {200}}</math>
<!-- everything beyond is technically not exact, but googologically almost identical -->
*<math>100\uparrow\uparrow 4=(10\uparrow)^2 (2 \times 10^ {200}+0.3)=(10\uparrow)^2 (2\times 10^ {200})=(10\uparrow)^3 200.3=(10\uparrow)^4 2.3</math>
*<math>100\uparrow\uparrow n=(10\uparrow)^{n-2} (2 \times 10^ {200})=(10\uparrow)^{n-1} 200.3=(10\uparrow)^{n}2.3<10\uparrow\uparrow (n+1)</math> (thus if ''n'' is large it seems fair to say that <math>100\uparrow\uparrow n</math> is "approximately equal to" <math>10\uparrow\uparrow n</math>)
*<math>100\uparrow\uparrow\uparrow 2=(10\uparrow)^{98} (2 \times 10^ {200})=(10\uparrow)^{100} 2.3</math>
*<math>100\uparrow\uparrow\uparrow 3=10\uparrow\uparrow(10\uparrow)^{98} (2 \times 10^ {200})=10\uparrow\uparrow(10\uparrow)^{100} 2.3</math>
*<math>100\uparrow\uparrow\uparrow n=(10\uparrow\uparrow)^{n-2}(10\uparrow)^{98} (2 \times 10^ {200})=(10\uparrow\uparrow)^{n-2}(10\uparrow)^{100} 2.3<10\uparrow\uparrow\uparrow (n+1)</math> (compare <math>10\uparrow\uparrow\uparrow n=(10\uparrow\uparrow)^{n-2}(10\uparrow)^{10}1<10\uparrow\uparrow\uparrow (n+1)</math>; thus if ''n'' is large it seems fair to say that <math>100\uparrow\uparrow\uparrow n</math> is "approximately equal to" <math>10\uparrow\uparrow\uparrow n</math>)
*<math>100\uparrow\uparrow\uparrow\uparrow 2=(10\uparrow\uparrow)^{98}(10\uparrow)^{100} 2.3</math> (compare <math>10\uparrow\uparrow\uparrow\uparrow 2=(10\uparrow\uparrow)^{8}(10\uparrow)^{10}1</math>)
*<math>100\uparrow\uparrow\uparrow\uparrow 3=10\uparrow\uparrow\uparrow(10\uparrow\uparrow)^{98}(10\uparrow)^{100} 2.3</math> (compare <math>10\uparrow\uparrow\uparrow\uparrow 3=10\uparrow\uparrow\uparrow(10\uparrow\uparrow)^{8}(10\uparrow)^{10}1</math>)
*<math>100\uparrow\uparrow\uparrow\uparrow n=(10\uparrow\uparrow\uparrow)^{n-2}(10\uparrow\uparrow)^{98}(10\uparrow)^{100} 2.3</math> (compare <math>10\uparrow\uparrow\uparrow\uparrow n=(10\uparrow\uparrow\uparrow)^{n-2}(10\uparrow\uparrow)^{8}(10\uparrow)^{10}1</math>; if ''n'' is large this is "approximately" equal)

== Accuracy ==

For a number <math>10^n</math>, one unit change in ''n'' changes the result by a factor 10. In a number like <math>10^{\,\!6.2 \times 10^3}</math>, with the 6.2 the result of proper rounding using significant figures, the true value of the exponent may be 50 less or 50 more. Hence the result may be a factor <math>10^{50}</math> too large or too small. This seems like extremely poor accuracy, but for such a large number it may be considered fair (a large error in a large number may be "relatively small" and therefore acceptable).

=== For very large numbers ===

In the case of an approximation of an extremely large number, the relative error may be large, yet there may still be a sense in which one wants to consider the numbers as "close in magnitude". For example, consider

:<math>10^{10}</math> and <math>10^9</math>

The relative error is

:<math>1 - \frac{10^9}{10^{10}} = 1 - \frac{1}{10} = 90\%</math>

a large relative error. However, one can also consider the relative error in the logarithms; in this case, the logarithms (to base 10) are 10 and 9, so the relative error in the logarithms is only 10%.

The point is that [[Exponential function|exponential function]]s magnify relative errors greatly – if ''a'' and ''b'' have a small relative error,

:<math>10^a</math> and <math>10^b</math>

the relative error is larger, and

:<math>10^{10^a}</math> and <math>10^{10^b}</math>

will have an even larger relative error. The question then becomes: on which level of iterated logarithms to compare two numbers? There is a sense in which one may want to consider

:<math>10^{10^{10}}</math> and <math>10^{10^9}</math>

to be "close in magnitude". The relative error between these two numbers is large, and the relative error between their logarithms is still large; however, the relative error in their second-iterated logarithms is small:

:<math>\log_{10}(\log_{10}(10^{10^{10}})) = 10</math> and <math>\log_{10}(\log_{10}(10^{10^9})) = 9</math>

Such comparisons of iterated logarithms are common, e.g., in [[Analytic number theory|analytic number theory]].

=== Classes ===
One solution to the problem of comparing large numbers is to define classes of numbers, such as the system devised by Robert Munafo,<ref>{{Cite web|title=Large Numbers at MROB|url=http://www.mrob.com/pub/math/largenum.html#classes|access-date=2021-05-13|website=www.mrob.com}}</ref> which is based on different "levels" of perception of an average person. Class 0 – numbers between zero and six – is defined to contain numbers that are easily [[Subitizing|subitized]], that is, numbers that show up very frequently in daily life and are almost instantly comparable. Class 1 – numbers between six and 1,000,000=10{{sup|6}} – is defined to contain numbers whose decimal expressions are easily subitized, that is, numbers who are easily comparable not by [[Cardinality|cardinality]], but "at a glance" given the decimal expansion.

Each class after these are defined in terms of iterating this base-10 exponentiation, to simulate the effect of another "iteration" of human indistinguishability. For example, class 5 is defined to include numbers between 10{{Sup|10{{sup|10{{sup|10{{sup|6}}}}}}}} and 10{{Sup|10{{sup|10{{sup|10{{sup|10{{sup|6}}}}}}}}}}, which are numbers where {{Var|X}} becomes humanly indistinguishable from {{Var|X}}{{Sup|2}} <ref>{{Cite web|title=Large Numbers (page 2) at MROB|url=http://www.mrob.com/pub/math/largenum-2.html#class5|access-date=2021-05-13|website=www.mrob.com}}</ref> (taking iterated logarithms of such {{Var|X}} yields indistinguishibility firstly between log({{Var|X}}) and 2log({{Var|X}}), secondly between log(log({{Var|X}})) and 1+log(log({{Var|X}})), and finally an extremely long decimal expansion whose length can't be subitized).

===Approximate arithmetic===

There are some general rules relating to the usual arithmetic operations performed on very large numbers:

*The sum and the product of two very large numbers are both "approximately" equal to the larger one.
*<math>(10^a)^{\,\!10^b}=10^{a 10^b}=10^{10^{b+\log _{10} a}}</math>
Hence:
*A very large number raised to a very large power is "approximately" equal to the larger of the following two values: the first value and 10 to the power the second. For example, for very large <math>n</math> there is <math>n^n\approx 10^n</math> (see e.g. the computation of mega) and also <math>2^n\approx 10^n</math>. Thus <math>2\uparrow\uparrow 65536 \approx 10\uparrow\uparrow 65533</math>, see [[Knuth's up-arrow notation#Tables of values|table]].

==Systematically creating ever-faster-increasing sequences==

Given a strictly increasing integer sequence/function <math>f_0(n)</math> (''n''≥1), it is possible to produce a faster-growing sequence <math>f_1(n) = f_0^n(n)</math> (where the superscript ''n'' denotes the ''n''<sup>th</sup> functional power). This can be repeated any number of times by letting <math>f_k(n) = f_{k-1}^n(n)</math>, each sequence growing much faster than the one before it. Thus it is possible to define <math>f_\omega(n) = f_n(n)</math>, which grows much faster than any <math>f_k</math> for finite ''k'' (here ω is the first infinite [[Ordinal number|ordinal number]], representing the limit of all finite numbers k).  This is the basis for the fast-growing hierarchy of functions, in which the indexing subscript is extended to ever-larger ordinals.

For example, starting with  ''f''<sub>0</sub>(''n'') = ''n'' + 1:

* ''f''<sub>1</sub>(''n'') = ''f''<sub>0</sub><sup>''n''</sup>(''n'') = ''n'' + ''n'' = 2''n''
* ''f''<sub>2</sub>(''n'') = ''f''<sub>1</sub><sup>''n''</sup>(''n'') = 2<sup>''n''</sup>''n'' > (2 ↑) ''n'' for n ≥ 2 (using Knuth up-arrow notation)
* ''f''<sub>3</sub>(''n'') = ''f''<sub>2</sub><sup>''n''</sup>(''n'') > (2 ↑)<sup>''n''</sup> ''n'' ≥ 2 ↑<sup>2</sup> ''n'' for ''n'' ≥ 2
* ''f''<sub>''k''+1</sub>(''n'') > 2 ↑<sup>''k''</sup> ''n'' for ''n'' ≥ 2, ''k'' < ω
* ''f''<sub>ω</sub>(''n'') = ''f''<sub>''n''</sub>(''n'') > 2 ↑<sup>''n'' – 1</sup> ''n'' > 2 ↑<sup>''n'' − 2</sup> (''n'' + 3) − 3 = ''A''(''n'', ''n'') for ''n'' ≥ 2, where ''A'' is the [[Ackermann function]] (of which ''f''<sub>ω</sub> is a unary version)
* ''f''<sub>ω+1</sub>(64) > ''f''<sub>ω</sub><sup>64</sup>(6) > [[Graham's number#Definition|Graham's number]] (= ''g''<sub>64</sub> in the sequence defined by ''g''<sub>0</sub> = 4, ''g''<sub>''k''+1</sub> = 3 ↑<sup>''g''<sub>''k''</sub></sup> 3)
**This follows by noting ''f''<sub>ω</sub>(''n'') > 2 ↑<sup>''n'' – 1</sup> ''n'' > 3 ↑<sup>''n'' – 2</sup> 3 + 2, and hence ''f''<sub>ω</sub>(''g''<sub>''k''</sub> + 2) > ''g''<sub>''k''+1</sub> + 2
* ''f''<sub>ω</sub>(''n'') > 2 ↑<sup>''n'' – 1</sup> ''n'' =  (2 → ''n'' → ''n''-1)  =  (2 → ''n'' → ''n''-1 → 1) (using [[Conway chained arrow notation]])
* ''f''<sub>ω+1</sub>(''n'') = ''f''<sub>ω</sub><sup>''n''</sup>(''n'') > (2 → ''n'' → ''n''-1 → 2) (because if ''g''<sub>''k''</sub>(''n'') = X → ''n'' → ''k'' then X → ''n'' → ''k''+1 = ''g''<sub>''k''</sub><sup>''n''</sup>(1))
* ''f''<sub>ω+''k''</sub>(''n'') > (2 → ''n'' → ''n''-1 → ''k''+1) > (''n'' → ''n'' → ''k'')
* ''f''<sub>ω2</sub>(''n'') = ''f''<sub>ω+''n''</sub>(''n'') > (''n'' → ''n'' → ''n'') = (''n'' → ''n'' → ''n''→ 1)
* ''f''<sub>ω2+''k''</sub>(''n'') > (''n'' → ''n'' → ''n'' → ''k'')
* ''f''<sub>ω3</sub>(''n'') > (''n'' → ''n'' → ''n'' → ''n'')
* ''f''<sub>ω''k''</sub>(''n'') > (''n'' → ''n'' → ... → ''n'' → ''n'') (Chain of ''k''+1 ''n'''s)
* ''f''<sub>ω<sup>2</sup></sub>(''n'') = ''f''<sub>ω''n''</sub>(''n'')  > (''n'' → ''n'' → ... → ''n'' → ''n'') (Chain of ''n''+1 ''n'''s)
{{mvar|}}

== In some noncomputable sequences ==

The [[Busy beaver|busy beaver]] function Σ is an example of a function which grows faster than any computable function. Its value for even relatively small input is huge. The values of Σ(''n'') for ''n'' = 1, 2, 3, 4, 5 are 1, 4, 6, 13, 4098<ref>{{Cite web |date=2024-07-02 |title=[July 2nd 2024] We have proved "BB(5) = 47,176,870" |url=https://discuss.bbchallenge.org/t/july-2nd-2024-we-have-proved-bb-5-47-176-870/237 |access-date=2024-07-04 |website=The Busy Beaver Challenge |language=en}}</ref> {{OEIS|id=A028444}}. Σ(6) is not known but is at least 10↑↑15.

== Infinite numbers ==

Although all the numbers discussed above are very large, they are all still [[Finite set|finite]]. Certain fields of mathematics define [[Infinity|infinite]] and [[Transfinite number|transfinite number]]s. For example, aleph-null is the [[Cardinality|cardinality]] of the [[Infinite set|infinite set]] of [[Natural number|natural number]]s, and aleph-one is the next greatest cardinal number. <math>\mathfrak{c}</math> is the [[Cardinality of the continuum|cardinality of the reals]].  The proposition that <math>\mathfrak{c} = \aleph_1</math> is known as the [[Continuum hypothesis|continuum hypothesis]].

== See also ==
* {{Annotated link|Arbitrary-precision arithmetic}}
* {{Annotated link|Dirac large numbers hypothesis}}
* {{Annotated link|Exponential growth}}
* {{Annotated link|History of large numbers}}
* {{Annotated link|Human scale}}
* {{Annotated link|Indefinite and fictitious numbers}}
* {{Annotated link|Indian numbering system}}
* {{Annotated link|Infinity}}
* {{Annotated link|Law of large numbers}}
* {{Annotated link|List of arbitrary-precision arithmetic software}}
* {{Annotated link|Long and short scales}}
* {{Annotated link|Myriad}}
* {{Annotated link|Names of large numbers}}
* {{Annotated link|Orders of magnitude}}
* {{Annotated link|Power of 10}}
* {{Annotated link|Power of two}}
* {{Annotated link|Tetration}}

==References==
{{Reflist}}

== External links ==

* [https://www.youtube.com/playlist?list=PL3A50BB9C34AB36B3 Ridiculously Huge Numbers] lecture series by David Metzler
{{Large numbers}}
{{Hyperoperations}}

[[Category:Large numbers| ]]
[[Category:Mathematical notation]]

{{Sourceattribution|Large numbers}}