Let $\mathcal{ A}$ be the set of all integers of the form $\gcd(n, F_n)$, where $n$ is a positive integer and $F_n$ denotes the $n$th Fibonacci number. Leonetti and Sanna proved that $\mathcal{ A}$ has natural density equal to zero, and asked for a more precise upper bound. We prove that \begin{ equation*} \#\big(\mathcal{ A} \cap [1, x]\big) \ll \frac{ x \log \log \log x}{ \log \log x} \end{ equation*} for all sufficiently large $x$.
Categories: math.NT