A row of lockers starts with all lockers closed. A person walks by and opens every locker. A second person walks by and closes every other locker, starting with locker 2. A third person walks by and changes the state of every third locker, starting with locker 3. This continues up to an person changing the locker. Which lockers are open and which are shut after people pass by? This Demonstration illustrates this problem with .

Contributed by: Marc Brodie (Wheeling Jesuit University)

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I first found this locker problem in G. L. Musser and W. F. Burger, Mathematics for Elementary Teachers: A Contemporary Approach, 4th ed., New York: John Wiley and Sons, 1996.