Primality proof for n = 21384809:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=11987.html>11987 is prime.</a>
<br>b^((n-1)/11987)-1 mod n = 19585778, which is a unit, inverse 9302612.
<p>(11987) divides n-1.
<p>(11987)^2 > n.
<p>n is prime by Pocklington's theorem.