Project Euler #92: Square digit chains

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    We should try to think the reverse solution. For eg. we have to get 89 using squares of numbers (1-9). Obtain 89 using 1, 4, 9, 16, 25, 36, 49, 64, 81 once or more than once. eg. 4+4+81=89 (the numbers are permutations of 2,9,2,0,0,0,0,0,0,0) use recursion and count