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Show that if $x, y, z$ are positive integers, then $(xy + 1)(yz + 1)(zx + 1)$ is a perfect square if and only if $xy + 1, yz + 1, zx+1$ are perfect squares.

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    Intriguing but not informative title...2011-12-17
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    googling (xy + 1)(yz + 1)(zx + 1) gives http://www.jstor.org/stable/26913472011-12-17
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    @sdcvvc, maybe you can summarize the contents of that paper here so that the question doesn't remain unanswered.2011-12-18

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