Take b = 2.

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

19 is prime.

b^((n-1)/19)-1 mod n = 8557, which is a unit, inverse 8344.

11 is prime.

b^((n-1)/11)-1 mod n = 8768, which is a unit, inverse 798.

(11 * 19) divides n-1.

(11 * 19)^2 > n.

n is prime by Pocklington's theorem.