Ulam Spiral : Sieve of Eratosthenes

Ulam Spiral
Using Sieve of Eratosthenes is WAY faster then Trial Devision (how I found primes before).  Using this I found all primes less then 6,553,600 in less then 2 seconds.  It took only 3 seconds total to generate the 2560x2560 PNG I'm now using as a desktop background.