Take b = 2.

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

331 is prime.

b^((n-1)/331)-1 mod n = 43427, which is a unit, inverse 87323.

17 is prime.

b^((n-1)/17)-1 mod n = 122808, which is a unit, inverse 40379.

(17 * 331) divides n-1.

(17 * 331)^2 > n.

n is prime by Pocklington's theorem.