Primes / Is 257 prime?

Is 257 a Prime Number?

Yes

257 is prime: for 257, testing every prime up to √257 ≈ 16.0 (namely 2, 3, 5, 7, 11, 13) finds no divisor. 257 sits between primes 251 and 263, 6 below and 6 above. 257 shares no factor with 2-12; 257's divisors start beyond that range. 257 is odd, digit sum 14 for 257, digital root 5 for 257. 257 has 3 primes within 10 of 257.