Primality proof for n = 1613:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=13.html>13 is prime.</a>
<br>b^((n-1)/13)-1 mod n = 125, which is a unit, inverse 942.
<p><a href=2.html>2 is prime.</a>
<br>b^((n-1)/2)-1 mod n = 1611, which is a unit, inverse 806.
<p>(2^2 * 13) divides n-1.
<p>(2^2 * 13)^2 > n.
<p>n is prime by Pocklington's theorem.