Primality proof for n = 1389386771:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=767617.html>767617 is prime.</a>
<br>b^((n-1)/767617)-1 mod n = 494935008, which is a unit, inverse 1058683819.
<p>(767617) divides n-1.
<p>(767617)^2 > n.
<p>n is prime by Pocklington's theorem.