a unit disk on each point whose number is odd. The diameter of these graphs, and the length of the solution to the standard form of the Tower of Hanoi puzzle (in which the disks all start on one tower and must all move to one other tower) is . More than three towers For , the structure of the Hanoi graphs is not as well understood, and the diameter of these graphs is unknown. When and or when and , these graphs are nonplanar. See also Sierpinski triangle References Parametric families of graphs Planar graphs