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Find the minimum positive integer

Source: 2013 China Mathematical Olympaid P6

January 14, 2013
abstract algebramodular arithmeticnumber theory proposednumber theory

Problem Statement

Let m,nm,n be positive integers. Find the minimum positive integer NN which satisfies the following condition. If there exists a set SS of integers that contains a complete residue system module mm such that S=N| S | = N, then there exists a nonempty set ASA \subseteq S so that nxAxn\mid {\sum\limits_{x \in A} x }.