Do there exist integers , and such that , , are perfect squares?
Solution
No. Suppose the contrary that there are such integers , and .
If one of them is even, say , then , which contradicts the assumption that is a perfect square. We may then assume that , and are odd, so they are either or . It follows from the Pigeon-hole Principle that two of them are congruent modulo . Relabel if necessary, we may assume that , so , which violates the perfect square assumption.
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