Primality proof for n = 20693:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=739.html>739 is prime.</a>
<br>b^((n-1)/739)-1 mod n = 5859, which is a unit, inverse 3606.
<p>(739) divides n-1.
<p>(739)^2 > n.
<p>n is prime by Pocklington's theorem.