Primality proof for n = 2221:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=37.html>37 is prime.</a>
<br>b^((n-1)/37)-1 mod n = 979, which is a unit, inverse 152.
<p><a href=5.html>5 is prime.</a>
<br>b^((n-1)/5)-1 mod n = 329, which is a unit, inverse 2194.
<p>(5 * 37) divides n-1.
<p>(5 * 37)^2 > n.
<p>n is prime by Pocklington's theorem.