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VMO 2022 problem 4 day 1

Source: Vietnam Mathematical Olympiad 2022 problem 4 day 1

March 4, 2022
vmonumber theoryDivisibility

Problem Statement

For every pair of positive integers (n,m)(n,m) with n<mn<m, denote s(n,m)s(n,m) be the number of positive integers such that the number is in the range [n,m][n,m] and the number is coprime with mm. Find all positive integers m2m\ge 2 such that mm satisfy these condition: i) s(n,m)mns(1,m)m\frac{s(n,m)}{m-n} \ge \frac{s(1,m)}{m} for all n=1,2,...,m1n=1,2,...,m-1; ii) 2022m+12022^m+1 is divisible by m2m^2