My Hanoi Tower app for iPhone and iPad

The Tower of Hanoi a.k.a the Tower of Brahma or Lucas Tower, is a logic game. It consists of three rods, and a number of disks of different sizes. The game starts with the disks in a stack in ascending order of size on one rod, the smallest at the top, hence making it look like a conical shape.
The goal of the puzzle is to move the entire stack to another rod, obeying the following simple rules:
Only one disk can be moved at a time.
A disk can only be moved if it is the uppermost disk on a stack.
No any disk can be placed on top of a smaller disk.
With three disks, the puzzle can be solved in seven moves. The minimum number of moves required to solve the puzzle is 2n - 1, where n is the number of disks.