Primes / Is 521 prime?

Is 521 a Prime Number?

Yes

521 is prime: for 521, testing every prime up to √521 ≈ 22.8 (namely 2, 3, 5, 7, 11, 13, 17, 19) finds no divisor. 521 sits between primes 509 and 523, 12 below and 2 above. 521 shares no factor with 2-12; 521's divisors start beyond that range. 521 is odd, digit sum 8 for 521, digital root 8 for 521. 521 has 2 primes within 10 of 521.