Primality proof for n = 68521:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=571.html>571 is prime.</a>
<br>b^((n-1)/571)-1 mod n = 34861, which is a unit, inverse 36400.
<p>(571) divides n-1.
<p>(571)^2 > n.
<p>n is prime by Pocklington's theorem.