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Problem 6 of RMO 2006 (Regional Mathematical Olympiad-India)

Source: Elementry Number Theory

September 13, 2009
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Problem Statement

Prove that there are infinitely many positive integers n n such that n(n\plus{}1) can be represented as a sum of two positive squares in at least two different ways. (Here a^{2}\plus{}b^{2} and b^{2}\plus{}a^{2} are considered as the same representation.)