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.