Primality proof for n = 20593:
<p>Take b = 5.
<p>b^(n-1) mod n = 1.
<p><a href=13.html>13 is prime.</a>
<br>b^((n-1)/13)-1 mod n = 13172, which is a unit, inverse 1862.
<p><a href=11.html>11 is prime.</a>
<br>b^((n-1)/11)-1 mod n = 20039, which is a unit, inverse 1301.
<p><a href=3.html>3 is prime.</a>
<br>b^((n-1)/3)-1 mod n = 142, which is a unit, inverse 6816.
<p>(3^2 * 11 * 13) divides n-1.
<p>(3^2 * 11 * 13)^2 > n.
<p>n is prime by Pocklington's theorem.