257 (number)

From Wikipedia, the free encyclopedia

257 is the natural number between 256 and 258. It is also a prime number.

← 256
258 →
257
Cardinal two hundred [and] fifty-seven
Ordinal 257th
(two hundred [and] fifty-seventh)
Factorization prime
Roman numeral CCLVII
Binary 100000001
Octal 401
Duodecimal 195
Hexadecimal 101

[edit] In mathematics

257 is a prime number of the form 2^{2^3}+1 and therefore a Fermat prime. It is currently the second largest known Fermat prime. It is also a Proth prime. And since it is of the form 4n + 1, it is a Pythagorean prime.

It is also an irregular prime, and a long prime (in base 10) and a balanced prime. Since the next prime, 263, is 6 away, 257 is called a sexy prime.

Since 257 + 2 = 259, a semiprime, 257 is a Chen prime. It is also an Eisenstein prime with no imaginary part, and a Pierpont prime.

[edit] In other fields

257 is the country calling code for Burundi. See List of country calling codes.