Take b = 2.

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

67 is prime.

b^((n-1)/67)-1 mod n = 4252, which is a unit, inverse 4505.

47 is prime.

b^((n-1)/47)-1 mod n = 1576, which is a unit, inverse 5040.

(47 * 67) divides n-1.

(47 * 67)^2 > n.

n is prime by Pocklington's theorem.