Primality proof for n = 2916841:

Take b = 3.

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

223 is prime.
b^((n-1)/223)-1 mod n = 1906604, which is a unit, inverse 1517285.

109 is prime.
b^((n-1)/109)-1 mod n = 1472766, which is a unit, inverse 2690537.

(109 * 223) divides n-1.

(109 * 223)^2 > n.

n is prime by Pocklington's theorem.