arXiv2017
Let $q > 2$ be a prime number and define $λ_q := \left( \fracτ{q} \right)$ where $τ(n)$ is the number of divisors of $n$ and $\left( \frac{\cdot}{q} \right)$ is the Legendre symbol. When $τ(n)$ is a quadratic residue modulo $q$, then $\left( λ_q \star \mathbf{1} \right) (n)$ could be close to the number of divisors of $n$. This is the aim of this work to compare the mean value of the function $λ_q \star \mathbf{1}$ to the well known average order of $τ$. The proof reveals that the results depend heavily on the value of $\left( \frac{2}{q} \right)$. A bound for short sums in the case $q=5$ is also given, using profound results from the theory of integer points close to certain smooth curves.