# 239 (number)

Short description: Natural number
 ← 238 239 240 →
Cardinaltwo hundred thirty-nine
Ordinal239th
(two hundred thirty-ninth)
Factorizationprime
Primeyes
Greek numeralΣΛΘ´
Roman numeralCCXXXIX
Binary111011112
Ternary222123
Quaternary32334
Quinary14245
Senary10356
Octal3578
Duodecimal17B12
VigesimalBJ20
Base 366N36

239 (two hundred [and] thirty-nine) is the natural number following 238 and preceding 240.

## In mathematics

It is a prime number. The next is 241, with which it forms a pair of twin primes; hence, it is also a Chen prime. 239 is a Sophie Germain prime and a Newman–Shanks–Williams prime.[1] It is an Eisenstein prime with no imaginary part and real part of the form 3n − 1 (with no exponentiation implied). 239 is also a happy number.

239 is the smallest positive integer d such that the imaginary quadratic field Q(d) has class number = 15.[2]

HAKMEM (incidentally AI memo 239 of the MIT AI Lab) included an item on the properties of 239, including these:[3]

• When expressing 239 as a sum of square numbers, 4 squares are required, which is the maximum that any integer can require; it also needs the maximum number (9) of positive cubes (23 is the only other such integer), and the maximum number (19) of fourth powers.[4]
• 239/169 is a convergent of the continued fraction of the square root of 2, so that 2392 = 2 · 1692 − 1.
• Related to the above, π/4 rad = 4 arctan(1/5) − arctan(1/239) = 45°.
• 239 · 4649 = 1111111, so 1/239 = 0.0041841 repeating, with period 7.
• 239 can be written as bn − bm − 1 for b = 2, 3, and 4, a fact evidenced by its binary representation 11101111, ternary representation 22212, and quaternary representation 3233.
• There are 239 primes < 1500.
• 239 is the largest integer n whose factorial can be written as the product of distinct factors between n + 1 and 2n, both included.[5]
• The only solutions of the Diophantine equation y2 + 1 = 2x4 in positive integers are (x, y) = (1, 1) or (13, 239).

## In other fields

239 is also:

• K239 is Mozart's only work for two orchestras.
• 239 is the atomic mass number of the most common isotope of plutonium, Pu-239
• 239 is an area code representing part of southwest Florida in the United States
• 239 is a world-famous lyceum of physics in mathematics in Saint-Petersburg, Russia .
• In The Simpsons episode "Homer's Night Out", Homer weighs himself and resolves to exercise. Six months later he weighs himself again and again resolves to exercise. Both times he weighed exactly 239 pounds. His weight was also seen in a daydream in the episode "King-Size Homer"