Consider a triangular pyramid of balls, constructed by placing each ball (except those on the bottom) in the hollow formed by the three balls under it. If such a pyramid has 12 balls on the side of the bottom level, how many balls in total does it contain?

12²+11²+10²+9²+8²+7²+6²+5²+4²+3²+2²+1 or 586

Posted by Eat Ham on 2002-08-05 11:13:42