Move all discs to the rightmost peg. Only one disc at a time, and never place a larger disc on a smaller one.
Easy
3 discs - minimum 7 moves required
Medium
4 discs - minimum 15 moves required
Hard
5 discs - minimum 31 moves required
Scientific Background
Based on: Tower of Hanoi / Tower of London Planning Tasks (Shallice & undefined, 1982)