Primality proof for n = 6857:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=857.html>857 is prime.</a>
<br>b^((n-1)/857)-1 mod n = 255, which is a unit, inverse 2205.
<p>(857) divides n-1.
<p>(857)^2 > n.
<p>n is prime by Pocklington's theorem.