Primality proof for n = 6521:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=163.html>163 is prime.</a>
<br>b^((n-1)/163)-1 mod n = 1043, which is a unit, inverse 3620.
<p>(163) divides n-1.
<p>(163)^2 > n.
<p>n is prime by Pocklington's theorem.