Primality proof for n = 134921:

Take b = 2.

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

3373 is prime.
b^((n-1)/3373)-1 mod n = 57396, which is a unit, inverse 125403.

(3373) divides n-1.

(3373)^2 > n.

n is prime by Pocklington's theorem.