Primality proof for n = 263:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=131.html>131 is prime.</a>
<br>b^((n-1)/131)-1 mod n = 3, which is a unit, inverse 88.
<p>(131) divides n-1.
<p>(131)^2 > n.
<p>n is prime by Pocklington's theorem.