The Locker Problem
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If we denote 0 as open and 1 as close, then we can see the pattern that the doors numbered in perfect squares - such as 1, 4, 9, 16, 25, 36, 49, ..., 961 - are close and the rest are open.
Therefore, the doors that are closed are: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576, 625, 676, 729, 784, 841, 900, and 961. The rest are open.
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