A generalization of Menon's identity with Dirichlet characters

TL;DR

This paper extends Menon's identity by incorporating Dirichlet characters, providing a more general formula that connects gcd sums with character sums and divisor functions, generalizing previous results.

Contribution

The paper introduces a generalized version of Menon's identity involving Dirichlet characters and multiple variables, extending prior work to broader cases.

Findings

Generalized Menon's identity with Dirichlet characters derived

Connected gcd sums with character sums and divisor functions

Extended previous results to cases with multiple variables and characters

Abstract

The classical Menon's identity [7] states that \begin{equation*}\label{oldbegin1} \sum_{\substack{a\in\Bbb Z_n^\ast }}\gcd(a -1,n)=\varphi(n) \sigma_{0} (n), \end{equation*} where for a positive integer $n$, $\Bbb Z_n^\ast$ is the group of units of the ring $\Bbb Z_n=\Bbb Z/n\Bbb Z$, $\gcd(\ ,\ )$ represents the greatest common divisor, $\varphi(n)$ is the Euler's totient function and $\sigma_{k} (n) =\sum_{d|n } d^{k}$ is the divisor function. In this paper, we generalize Menon's identity with Dirichlet characters in the following way: \begin{equation*} \sum_{\substack{a\in\Bbb Z_n^\ast b_1, ..., b_k\in\Bbb Z_n}} \gcd(a-1,b_1, ..., b_k, n)\chi(a)=\varphi(n)\sigma_k\left(\frac{n}{d}\right), \end{equation*} where $k$ is a non-negative integer and $\chi$ is a Dirichlet character modulo $n$ whose conductor is $d$. Our result can be viewed as an extension of Zhao and Cao's result [16] to $k>0$. It can also be viewed as an extension of Sury's result [12] to Dirichlet characters.