olymmath

JBMO-SL 2011 C5

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A set SS of natural numbers is called good, if for each element x∈S,xx \in S, x does not divide the sum of the remaining numbers in SS. Find the maximal possible number of elements of a good set which is a subset of the set A={1,2,3,…,63}A=\{1,2,3, \ldots, 63\}.

Dataset text NuminaMath olympiads. Quoted with source.

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