Primality proof for n = 20387630040577:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=1947073.html>1947073 is prime.</a>
<br>b^((n-1)/1947073)-1 mod n = 8781842158421, which is a unit, inverse 8827434988267.
<p><a href=401.html>401 is prime.</a>
<br>b^((n-1)/401)-1 mod n = 3886750572315, which is a unit, inverse 8110381387918.
<p>(401 * 1947073) divides n-1.
<p>(401 * 1947073)^2 > n.
<p>n is prime by Pocklington's theorem.