Primality proof for n = 402021673:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=1288531.html>1288531 is prime.</a>
<br>b^((n-1)/1288531)-1 mod n = 297945233, which is a unit, inverse 142086214.
<p>(1288531) divides n-1.
<p>(1288531)^2 > n.
<p>n is prime by Pocklington's theorem.