Take b = 2.

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

911 is prime.

b^((n-1)/911)-1 mod n = 16404668, which is a unit, inverse 18755503.

17 is prime.

b^((n-1)/17)-1 mod n = 12284545, which is a unit, inverse 15400954.

(17 * 911) divides n-1.

(17 * 911)^2 > n.

n is prime by Pocklington's theorem.