Take b = 2.

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

71 is prime.

b^((n-1)/71)-1 mod n = 13961, which is a unit, inverse 4037.

7 is prime.

b^((n-1)/7)-1 mod n = 36461, which is a unit, inverse 59952.

(7 * 71) divides n-1.

(7 * 71)^2 > n.

n is prime by Pocklington's theorem.