Primality proof for n = 113:
Take b = 3.
b^(n-1) mod n = 1.
7 is prime.
b^((n-1)/7)-1 mod n = 48, which is a unit, inverse 73.
2 is prime.
b^((n-1)/2)-1 mod n = 111, which is a unit, inverse 56.
(2^4 * 7) divides n-1.
(2^4 * 7)^2 > n.
n is prime by Pocklington's theorem.