Take b = 2.

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

13 is prime.

b^((n-1)/13)-1 mod n = 2590, which is a unit, inverse 2189.

7 is prime.

b^((n-1)/7)-1 mod n = 2224, which is a unit, inverse 2147.

(7^2 * 13) divides n-1.

(7^2 * 13)^2 > n.

n is prime by Pocklington's theorem.