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There is a,b in S where b divides 2a

Source: 2012 Indonesia Round 2.5 TST 1 Problem 2

May 10, 2012
combinatorics unsolvedcombinatorics

Problem Statement

Suppose SS is a subset of {1,2,3,…,2012}\{1,2,3,\ldots,2012\}. If SS has at least 10001000 elements, prove that SS contains two different elements a,ba,b, where bb divides 2a2a.
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