Primality proof for n = 67280421310721:
<p>Take b = 3.
<p>b^(n-1) mod n = 1.
<p><a href=2998279.html>2998279 is prime.</a>
<br>b^((n-1)/2998279)-1 mod n = 61150258807255, which is a unit, inverse 47000331560307.
<p><a href=373.html>373 is prime.</a>
<br>b^((n-1)/373)-1 mod n = 65541179653180, which is a unit, inverse 20076373578344.
<p>(373 * 2998279) divides n-1.
<p>(373 * 2998279)^2 > n.
<p>n is prime by Pocklington's theorem.