Primality proof for n = 215531:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=3079.html>3079 is prime.</a>
<br>b^((n-1)/3079)-1 mod n = 82144, which is a unit, inverse 55827.
<p>(3079) divides n-1.
<p>(3079)^2 > n.
<p>n is prime by Pocklington's theorem.