The summatory function of the Möbius function involving the greatest common divisor

Abstract: Let $\gcd(m,n)$ denote the greatest common divisor of the positive integers $m$ and $n$, and let $\mu$ represent the M\" obius function. For any real number $x>5$, we define the summatory function of the M\" obius function involving the greatest common divisor as $ S_{\mu}(x) := \sum_{mn\leq x} \mu(\gcd(m,n)). $ In this paper, we present an asymptotic formula for $S_{\mu}(x)$. Assuming the Riemann Hypothesis, we delve further into the asymptotic behavior of $S_{\mu}(x)$ and derive a mean square estimate for its error term. Our proof employs the Perron formula, Parseval's theorem, complex integration techniques, and the properties of the Riemann zeta-function.