In this puzzle or brainteaser, you are supposed to turn off the lights of houses with a growing number of windows : 4,9,16,25, etc. There are six houses, or six levels. Turning a light on or off turns some other lights on or off, according to a very simple pattern. The first three levels are quite easy. Even a small child can solve them by trial and error. Then you need to think and find a method. All the levels can be solved