http://www.scriptol.org/sieve.php#python http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes (watch graphic, we actually use the Sieve of Atkin) http://www.fermi.franken.de/wschildbach/primes.html Ulam Spiral http://ourworld.cs.com/ttpi314159/index.htm?f=fs php implementation, finding location (x,y) of a prime http://mgccl.com/taxonomy/term/20/0?page=3 http://krenzel.info/?p=81 http://www.ocf.berkeley.edu/~wwu/riddles/cs.shtml#numberSpiral