Primality proof for n = 4019:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=41.html>41 is prime.</a>
<br>b^((n-1)/41)-1 mod n = 3335, which is a unit, inverse 3026.
<p><a href=7.html>7 is prime.</a>
<br>b^((n-1)/7)-1 mod n = 272, which is a unit, inverse 2438.
<p>(7^2 * 41) divides n-1.
<p>(7^2 * 41)^2 > n.
<p>n is prime by Pocklington's theorem.