Primality proof for n = 531581:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=3797.html>3797 is prime.</a>
<br>b^((n-1)/3797)-1 mod n = 32300, which is a unit, inverse 50673.
<p>(3797) divides n-1.
<p>(3797)^2 > n.
<p>n is prime by Pocklington's theorem.