Primality proof for n = 28793:
Take b = 2.
b^(n-1) mod n = 1.
61 is prime.
b^((n-1)/61)-1 mod n = 3211, which is a unit, inverse 11137.
59 is prime.
b^((n-1)/59)-1 mod n = 24801, which is a unit, inverse 11836.
(59 * 61) divides n-1.
(59 * 61)^2 > n.
n is prime by Pocklington's theorem.