Primes / Is 31 prime?

Is 31 a Prime Number?

Yes

31 is prime: for 31, testing every prime up to √31 ≈ 5.6 (namely 2, 3, 5) finds no divisor. 31 sits between primes 29 and 37, 2 below and 6 above. 31 shares no factor with 2-12; 31's divisors start beyond that range. 31 is odd, digit sum 4 for 31, digital root 4 for 31. 31 has 5 primes within 10 of 31.