1 Million Lockers

There are one million numbered lockers in a row. They all start out closed. On your first pass, you flip every locker, so each one is open. On your second pass, you flip every locker divisible by 2, so you close lockers 2, 4, 6, etc. On the third pass, you flip every locker divisible by 3, so locker 3 becomes closed, locker 6 becomes open, etc. You continue this pattern until the millionth pass, flipping only the millionth locker on the last pass. At the end, is the millionth locker open? What do all the open lockers have in common? Why?