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MathNet 2009-part-04 — 175 problems (EN–VI) Question 100

Math Olympiad Vault · MathNet 2009-part-04 — 175 problems (EN–VI)

Question 100

For every positive integer $m$ denote by $\sigma(m)$ the sum of all its divisors, and by $\phi(m)$ the number of positive integers less than $m$ and coprime with $m$. Prove that there exists infinitely many such positive integer numbers $n$ for which $\phi(\sigma(n)) \gt n$.