Primality proof for n = 131909:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=673.html>673 is prime.</a>
<br>b^((n-1)/673)-1 mod n = 120996, which is a unit, inverse 11350.
<p>(673) divides n-1.
<p>(673)^2 > n.
<p>n is prime by Pocklington's theorem.