http://io9.com/5819325/the-bizarre-mathematical-conundrum-of-ulams-spiral http://scienceblogs.com/goodmath/2010/06/the_surprises_never_eend_the_u.php http://img529.imageshack.us/img529/615/ulam3.png http://imprompt.us/2010/ulam-spiral-take-2/ http://home.manhattan.edu/~peter.boothe/ulam.pdf http://mathworld.wolfram.com/PrimeSpiral.html ...