The University of Tennessee at Martin: Chris K. Caldwell's "Euclid's Proof of the Infinitude of Primes"

Read the entire webpage on Euclid's proof of the infinitude of primes. Be sure you understand why the prime $P$ is not already in the list of primes; if necessary, re-read this text a few times until you have fully grasped this concept.

Click http://web.archive.org/web/20160322095255/http://primes.utm.edu/notes/proofs/infinite/euclids.html link to open resource.