Take b = 2.

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

13 is prime.

b^((n-1)/13)-1 mod n = 233885, which is a unit, inverse 175999.

7 is prime.

b^((n-1)/7)-1 mod n = 113350, which is a unit, inverse 149429.

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

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

n is prime by Pocklington's theorem.