Take b = 2.

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

397 is prime.

b^((n-1)/397)-1 mod n = 49624731, which is a unit, inverse 92192976.

347 is prime.

b^((n-1)/347)-1 mod n = 128970448, which is a unit, inverse 133210330.

(347 * 397) divides n-1.

(347 * 397)^2 > n.

n is prime by Pocklington's theorem.