Primality proof for n = 3736981:

Take b = 2.

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

1597 is prime.
b^((n-1)/1597)-1 mod n = 2483303, which is a unit, inverse 960463.

13 is prime.
b^((n-1)/13)-1 mod n = 409531, which is a unit, inverse 351715.

(13 * 1597) divides n-1.

(13 * 1597)^2 > n.

n is prime by Pocklington's theorem.