Primality proof for n = 509:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=127.html>127 is prime.</a>
<br>b^((n-1)/127)-1 mod n = 15, which is a unit, inverse 34.
<p>(127) divides n-1.
<p>(127)^2 > n.
<p>n is prime by Pocklington's theorem.