Primality proof for n = 208393:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=457.html>457 is prime.</a>
<br>b^((n-1)/457)-1 mod n = 25691, which is a unit, inverse 50989.
<p>(457) divides n-1.
<p>(457)^2 > n.
<p>n is prime by Pocklington's theorem.