Note on a sum involving the Euler function

Abstract

We prove that $$ \sum_{n \leq x} φ([x/n])\leq\bigg(\frac{1380}{4009}+\frac{2629}{4009}\cdot\frac1{ζ(2)}+o(1)\bigg)x\log x $$ as $x\to\infty$, where $φ$ denotes the Euler totient function and $[x]$ denotes the integer part of $x$.

This paper has been combined with arXiv:1808.00188