Primality proof for n = 6418733:

Take b = 2.

b^(n-1) mod n = 1.

84457 is prime.
b^((n-1)/84457)-1 mod n = 2105383, which is a unit, inverse 1942126.

(84457) divides n-1.

(84457)^2 > n.

n is prime by Pocklington's theorem.