Take b = 2.

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

617 is prime.

b^((n-1)/617)-1 mod n = 1316979, which is a unit, inverse 1067062.

79 is prime.

b^((n-1)/79)-1 mod n = 949707, which is a unit, inverse 71110.

(79 * 617) divides n-1.

(79 * 617)^2 > n.

n is prime by Pocklington's theorem.