> Put n red stones then n green stones then n blue stones on a ring. At each step you can take any stone and hop it over a pair of adjacent stones of the same colour, in any direction around the ring. So for example, if you have ...rbb... then you can take the r stone and hop it over the bb pair. The question is: For what n is there a sequence of steps that rearranges the stones to be blue then green then red?