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George, Here is another simple approach to your type of problem. Just look for patterns. Call your number N. First ask yourself what the last digit of N must be must be for its square to end in 6. (For example, the square of any number ending in 3 or in 7 will end in 9: 13^{2} = 169, 23^{2} = 529, ... 17^{2} = 289...) You will quickly see that N must end in 6. Chris  


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