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3 divides no of lists of jointly coprime positive integer numbers that sum to n

Source: IMAR 2011 p4

September 27, 2018
number theorycoprimeSumdivisible

Problem Statement

Given an integer number n3n \ge 3, show that the number of lists of jointly coprime positive integer numbers that sum to nn is divisible by 33. (For instance, if n=4n = 4, there are six such lists: (3,1),(1,3),(2,1,1),(1,2,1),(1,1,2)(3, 1), (1, 3), (2, 1, 1), (1, 2, 1), (1, 1, 2) and (1,1,1,1)(1, 1, 1, 1).)