Take b = 2.

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

191 is prime.

b^((n-1)/191)-1 mod n = 1264407, which is a unit, inverse 386992.

151 is prime.

b^((n-1)/151)-1 mod n = 1043641, which is a unit, inverse 722802.

(151 * 191) divides n-1.

(151 * 191)^2 > n.

n is prime by Pocklington's theorem.