Take b = 2.

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

211 is prime.

b^((n-1)/211)-1 mod n = 342513, which is a unit, inverse 852476.

19 is prime.

b^((n-1)/19)-1 mod n = 540313, which is a unit, inverse 212940.

(19 * 211) divides n-1.

(19 * 211)^2 > n.

n is prime by Pocklington's theorem.