On the reciprocal sum of lcm of k-tuples

Abstract

We prove that the reciprocal sum $S_k(x)$ of the least common multiple of $k\geq 3$ positive integers in $\N\cap [1,x]$ satisfies $$ S_k(x)=P_{2^k-1}(\log x)+O(x^{-θ_k+ε}) $$ where $P$ is a polynomial of degree $2^k-1$ and $θ_k=\frac{2^k}{(k+1)^{\frac{k+1}2}}\cdot \frac3{2^k+6k-5}$. This was conjectured in Hilberdink, Luca, and Tóth~\cite[Remark 2.4]{HLT}. We also prove asymptotic formulas for similar sums conjectured there.