Primality proof for n = 39850487891:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=272333.html>272333 is prime.</a>
<br>b^((n-1)/272333)-1 mod n = 4150408928, which is a unit, inverse 20340756640.
<p>(272333) divides n-1.
<p>(272333)^2 > n.
<p>n is prime by Pocklington's theorem.