Note: The method used below is very slow, with 1bb iterations when trying to find 1000. For a faster method see: https://gist.github.com/jmervine/b5d985398b3ca7ba16aa (~125k iterations)
A Pythagorean triplet is a set of three natural numbers, a b c, for which,
a2 + b2 = c2 For example, 32 + 42 = 9 + 16 = 25 = 52.