olymmath

VMO 2022

Vietnam Mathematical Olympiad 2022.

Other problems

Problem 4

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 m≥2m\ge 2 such that mm satisfy these condition: i) s(n,m)m−n≥s(1,m)m\frac{s(n,m)}{m-n} \ge \frac{s(1,m)}{m} for all n=1,2,...,m−1n=1,2,...,m-1 ; ii) 2022m+12022^m+1 is divisible by m2m^2