Towers of Hanoi

The objective of the game is to move the entire stack of disks from Tower 1 to Tower 3.
You can move only one disk at a time. No disk may be placed on top of a smaller disk.
A disk is moved between the towers by Drag & Drop.

Tower 1    Tower 2    Tower 3
(Minimum number of moves to solve this puzzle is: 7 )        
Number of disks: