Primality proof for n = 3686357:

Take b = 2.

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

921589 is prime.
b^((n-1)/921589)-1 mod n = 15, which is a unit, inverse 1720300.

(921589) divides n-1.

(921589)^2 > n.

n is prime by Pocklington's theorem.