Take b = 3.

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

7 is prime. b^((n-1)/7)-1 mod n = 48, which is a unit, inverse 73.

2 is prime. b^((n-1)/2)-1 mod n = 111, which is a unit, inverse 56.

(2^4 * 7) divides n-1.

(2^4 * 7)^2 > n.

n is prime by Pocklington's theorem.