Take b = 2.

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

19211 is prime.

b^((n-1)/19211)-1 mod n = 2446132186, which is a unit, inverse 1684996232.

83 is prime.

b^((n-1)/83)-1 mod n = 1975856084, which is a unit, inverse 1992305034.

(83 * 19211) divides n-1.

(83 * 19211)^2 > n.

n is prime by Pocklington's theorem.