Short description: Natural number
- the 20th prime number. The next is 73, with which it composes a twin prime.
- a permutable prime with 17.
- is the largest number which occurs as a prime factor of an order of a sporadic simple group.
- the sum of three consecutive primes: 19, 23 and 29.
- a centered heptagonal number.
- an Eisenstein prime with no imaginary part and real part of the form 3n – 1.
- a Pillai prime, since 9! + 1 is divisible by 71 but 71 is not one more than a multiple of 9.
- the largest (15th) supersingular prime, which is also a Chen prime.
- part of the last known pair (71, 7) of Brown numbers, since 712 = 7! + 1.
- the twenty-third term of the Euclid–Mullin sequence, as it is the least prime factor of one more than the product of the first twenty-two terms.
- the smallest positive integer d such that the imaginary quadratic field Q(√) has class number = 7.
- the algebraic degree of Conway's constant, a remarkable number arising in the study of look-and-say sequences.
- the sum of primes less than 71 (2 through 67) is 568, which is divisible by 71.
- 71 is the only number between 1 and 100 that is one less or one more than divisible by all numbers from 2 to 10 (70: 2, 5, 7, 10) (72: 2, 3, 4, 6, 8, 9).
- 71 is an index of a prime Lucas number. 
- Messier object M71, a magnitude 8.5 globular cluster in the constellation Sagitta
- The New General Catalogue object NGC 71, a magnitude 13.2 peculiar spiral galaxy in the constellation Andromeda
In other fields
Seventy-one is also:
- The number of different characters that can be used with a standard English keyboard, excluding uppercase letters
- The registry of the U.S. Navy's nuclear aircraft carrier USS Theodore Roosevelt (CVN-71), named after U.S. President Theodore Roosevelt
- The number of the French department Saône-et-Loire
- The year AD 71, 71 BC, or 1971
- In the Mexican television sitcom, El Chavo del Ocho, Doña Clotilde lives in the apartment number 71, being therefore known as "La Bruja del 71" (Spanish: "The Witch from Number 71")
- Lockheed SR-71 Blackbird long-range, Mach 3 strategic reconnaissance aircraft
- 71 Fragments of a Chronology of Chance, a film by Michael Haneke
- 71: Into the Fire, South Korean film about the Korean War
- The form number for the United States Office of Personnel Management for requesting a leave of absence
- The Irish Rail 071 Class diesel locomotive
- In the Jason Bourne novels by American author Robert Ludlum the department within the CIA which made Bourne and the other super agents is called Treadstone Seventy-One.
- SR-71, an United States alternative rock band
- The number of the laps of the Austrian Grand Prix, Mexican Grand Prix, and Brazilian Grand Prix
- "Sloane's A069099 : Centered heptagonal numbers". OEIS Foundation. https://oeis.org/A069099.
- "Sloane's A063980 : Pillai primes". OEIS Foundation. https://oeis.org/A063980.
- "Sloane's A002267 : The 15 supersingular primes". OEIS Foundation. https://oeis.org/A002267.
- "Sloane's A000945 : Euclid-Mullin sequence". OEIS Foundation. https://oeis.org/A000945.
- "Tables of imaginary quadratic fields with small class number". http://www.numbertheory.org/classnos/.
- "Indices of prime Lucas numbers:". OEIS Foundation. https://oeis.org/A001606.
Original source: https://en.wikipedia.org/wiki/71 (number). Read more