Primality proof for n = 66891682553:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=21384809.html>21384809 is prime.</a>
<br>b^((n-1)/21384809)-1 mod n = 60851177397, which is a unit, inverse 32312831146.
<p>(21384809) divides n-1.
<p>(21384809)^2 > n.
<p>n is prime by Pocklington's theorem.