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{1...1}{5...5}6 is a perfect square (HOMC 2012 Q7)

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July 24, 2019
number theoryPerfect Square

Problem Statement

Prove that the number a=1...15...56a =\overline{{1...1}{5...5}6} is a perfect square (where 11s are 20122012 in total and 55s are 20112011 in total)