The Hundred Lockers
100 lockers are closed. Person 1 toggles every locker, person 2 every 2nd locker, person 3 every 3rd, and so on through person 100. After all 100 passes, how many lockers are open?
Related problems
Source: Classic locker-toggling parity puzzle in wide circulation; no traceable original source. Statement written for AxiomIQ.