\phi (n)+1 (not necessarily different) divisors n with the sum n
Source: 2021 Ukraine NMO 10.8 11.7
April 4, 2021
number theoryDivisors
Problem Statement
Given a natural number . Prove that you can choose (not necessarily different) divisors with the sum . Here denotes the number of natural numbers less than that are coprime with .(Fedir Yudin)