Show that there are only finitely many triples of positive integers satisfying the equation .
Solution
There are at most six permutations for any three numbers . It suffices to show that there are only finitely many triples , with , of positive integers satisfying the equation . It follows that or . Clearly, there are finitely many pairs of positive integers satisfying the equation and for each fixed pair of integers there is at most one positive integer satisfying the equation (because it is a linear equation in ).
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