Take b = 2.

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

17 is prime.

b^((n-1)/17)-1 mod n = 33402, which is a unit, inverse 12362.

13 is prime.

b^((n-1)/13)-1 mod n = 42375, which is a unit, inverse 3658.

(13 * 17) divides n-1.

(13 * 17)^2 > n.

n is prime by Pocklington's theorem.