Prove that for any positive integer there exist pairwise distinct integers for which the sum of their squares equals the sum of their cubes.
Solution
For any integer the numbers , , satisfy the conditions of the problem, because they are pairwise different and
With growing, the numbers in these triples get arbitrarily large, hence for any set of these triples one can find a new triple, where all numbers are larger than the ones already used.
Any positive integer can be written as with . Choose triples as above so that the numbers in them do not coincide. If , then add , and if , then add and . Since for each group the sum of the squares of the numbers equals the sum of the cubes of the numbers, the same property holds for the whole set.
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