Primality proof for n = 631:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=5.html>5 is prime.</a>
<br>b^((n-1)/5)-1 mod n = 227, which is a unit, inverse 467.
<p><a href=3.html>3 is prime.</a>
<br>b^((n-1)/3)-1 mod n = 42, which is a unit, inverse 616.
<p>(3^2 * 5) divides n-1.
<p>(3^2 * 5)^2 > n.
<p>n is prime by Pocklington's theorem.