Take b = 2.

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

661 is prime.

b^((n-1)/661)-1 mod n = 439848, which is a unit, inverse 311749.

53 is prime.

b^((n-1)/53)-1 mod n = 190015, which is a unit, inverse 427619.

(53 * 661) divides n-1.

(53 * 661)^2 > n.

n is prime by Pocklington's theorem.