Primality proof for n = 65537:

Take b = 3.

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

2 is prime.
b^((n-1)/2)-1 mod n = 65535, which is a unit, inverse 32768.

(2^16) divides n-1.

(2^16)^2 > n.

n is prime by Pocklington's theorem.