Take b = 2.

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

67 is prime.

b^((n-1)/67)-1 mod n = 2920, which is a unit, inverse 2617.

7 is prime.

b^((n-1)/7)-1 mod n = 1825, which is a unit, inverse 3249.

(7 * 67) divides n-1.

(7 * 67)^2 > n.

n is prime by Pocklington's theorem.