Primality proof for n = 39850487891:

Take b = 2.

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

272333 is prime.
b^((n-1)/272333)-1 mod n = 4150408928, which is a unit, inverse 20340756640.

(272333) divides n-1.

(272333)^2 > n.

n is prime by Pocklington's theorem.