Primality proof for n = 1687658803:

Take b = 2.

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

281276467 is prime.
b^((n-1)/281276467)-1 mod n = 63, which is a unit, inverse 857223519.

(281276467) divides n-1.

(281276467)^2 > n.

n is prime by Pocklington's theorem.