Primality proof for n = 8620289:
Take b = 2.
b^(n-1) mod n = 1.
223 is prime.
b^((n-1)/223)-1 mod n = 4858170, which is a unit, inverse 4776110.
151 is prime.
b^((n-1)/151)-1 mod n = 3461388, which is a unit, inverse 5838524.
(151 * 223) divides n-1.
(151 * 223)^2 > n.
n is prime by Pocklington's theorem.