Rules are the same as any polygonal number evolution, but you have to evolve both the number AND the polygon. The polygon needs to have 1 extra side, starting from the 1-gon (point) with the 1st 1-gonal number being 1. Then the 2nd 2-gonal (normal) number is 2, the 3rd 3-gonal (triangle) number is 6, etc. Basically, this sequence has all numbers that are the nth n-gonal number.
