Primality proof for n = 186766509188519991823:

Take b = 2.

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

294639853 is prime.
b^((n-1)/294639853)-1 mod n = 2877256809256278319, which is a unit, inverse 112338998508828700677.

285457 is prime.
b^((n-1)/285457)-1 mod n = 4736697137797038905, which is a unit, inverse 64989482143271511135.

(285457 * 294639853) divides n-1.

(285457 * 294639853)^2 > n.

n is prime by Pocklington's theorem.