Primality proof for n = 27457:
Take b = 2.
b^(n-1) mod n = 1.
13 is prime.
b^((n-1)/13)-1 mod n = 22508, which is a unit, inverse 18902.
11 is prime.
b^((n-1)/11)-1 mod n = 102, which is a unit, inverse 15882.
3 is prime.
b^((n-1)/3)-1 mod n = 3587, which is a unit, inverse 17108.
(3 * 11 * 13) divides n-1.
(3 * 11 * 13)^2 > n.
n is prime by Pocklington's theorem.