He does a peculiar thing. If there are n bulbs in a corridor, he walks along the corridor back and
forth n times. On the i-th walk, he toggles only the switch whose position is divisible by i. He does
not press any switch when coming back to his initial position. The i-th walk is defined as going
down the corridor (doing his peculiar thing) and coming back again. Determine the final state of the
last bulb. Is it on or off?