Primality proof for n = 272109983:
<p>Take b = 2.
<p>b^(n-1) mod n = 1.
<p><a href=421.html>421 is prime.</a>
<br>b^((n-1)/421)-1 mod n = 212077890, which is a unit, inverse 7756922.
<p><a href=233.html>233 is prime.</a>
<br>b^((n-1)/233)-1 mod n = 211714061, which is a unit, inverse 163678795.
<p>(233 * 421) divides n-1.
<p>(233 * 421)^2 > n.
<p>n is prime by Pocklington's theorem.