Take b = 2.

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

71 is prime.

b^((n-1)/71)-1 mod n = 16370, which is a unit, inverse 17522.

7 is prime.

b^((n-1)/7)-1 mod n = 18454, which is a unit, inverse 26942.

(7 * 71) divides n-1.

(7 * 71)^2 > n.

n is prime by Pocklington's theorem.