Primality proof for n = 991:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=11.html>11 is prime.</a>
<br>b^((n-1)/11)-1 mod n = 49, which is a unit, inverse 809.
<p><a href=5.html>5 is prime.</a>
<br>b^((n-1)/5)-1 mod n = 798, which is a unit, inverse 267.
<p>(5 * 11) divides n-1.
<p>(5 * 11)^2 > n.
<p>n is prime by Pocklington's theorem.