1998 USAMO Problems/Problem 5
Prove that for each , there is a set of integers such that divides for every distinct .
Proof by induction. For n=2, the proof is trivial, since satisfies the condition. Assume now that there is such a set S of n elements, which satisfy the condition. The key is to note that if , then if we define for all , where k is a positive integer, then and , and so .
Let . Consider the set . To finish the proof, we simply need to choose a k such that for all . Since , simply choose k so that .
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