Primality proof for n = 217003:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=613.html>613 is prime.</a>
<br>b^((n-1)/613)-1 mod n = 175150, which is a unit, inverse 143388.
<p>(613) divides n-1.
<p>(613)^2 > n.
<p>n is prime by Pocklington's theorem.