Primality proof for n = 20719:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=1151.html>1151 is prime.</a>
<br>b^((n-1)/1151)-1 mod n = 13515, which is a unit, inverse 14849.
<p>(1151) divides n-1.
<p>(1151)^2 > n.
<p>n is prime by Pocklington's theorem.