Primality proof for n = 127727:

Take b = 2.

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

63863 is prime.
b^((n-1)/63863)-1 mod n = 3, which is a unit, inverse 42576.

(63863) divides n-1.

(63863)^2 > n.

n is prime by Pocklington's theorem.