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.