Sums of Averages of GCD-Sum Functions II
AbstractLet $$ \gcd (k,j) $$ gcd ( k , j ) denote the greatest common divisor of the integers k and j, and let r be any fixed positive integer. Define $$\begin{aligned} M_r(x; f) := \sum _{k\le x}\frac{1}{k^{r+1}}\sum _{j=1}^{k}j^{r}f(\gcd (j,k)) \end{aligned}$$ M r ( x ; f ) : = ∑ k ≤ x 1 k r + 1 ∑ j = 1 k j r f ( gcd ( j , k ) ) for any large real number $$x\ge 5$$ x ≥ 5 , where f is any arithmetical function. Let $$\phi $$ ϕ , and $$\psi $$ ψ denote the Euler totient and the Dedekind function, respectively. In this paper, we refine asymptotic expansions of $$M_r(x; \mathrm{id})$$ M r ( x ; id ) , $$M_r(x;{\phi })$$ M r ( x ; ϕ ) and $$M_r(x;{\psi })$$ M r ( x ; ψ ) . Furthermore, under the Riemann Hypothesis and the simplicity of zeros of the Riemann zeta-function, we establish the asymptotic formula of $$M_r(x;\mathrm{id})$$ M r ( x ; id ) for any large positive number $$x>5$$ x > 5 satisfying $$x=[x]+\frac{1}{2}$$ x = [ x ] + 1 2 .