Primality proof for n = 43153393:
Take b = 2.
b^(n-1) mod n = 1.
1069 is prime.
b^((n-1)/1069)-1 mod n = 26996680, which is a unit, inverse 10239774.
29 is prime.
b^((n-1)/29)-1 mod n = 16879145, which is a unit, inverse 8206854.
(29^2 * 1069) divides n-1.
(29^2 * 1069)^2 > n.
n is prime by Pocklington's theorem.