Primality proof for n = 2420633:

Take b = 2.

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

302579 is prime.
b^((n-1)/302579)-1 mod n = 255, which is a unit, inverse 265795.

(302579) divides n-1.

(302579)^2 > n.

n is prime by Pocklington's theorem.