Primality proof for n = 1531:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=17.html>17 is prime.</a>
<br>b^((n-1)/17)-1 mod n = 501, which is a unit, inverse 492.
<p><a href=5.html>5 is prime.</a>
<br>b^((n-1)/5)-1 mod n = 224, which is a unit, inverse 745.
<p>(5 * 17) divides n-1.
<p>(5 * 17)^2 > n.
<p>n is prime by Pocklington's theorem.