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The classical system of functional equations      $1/n{\sum }_{\nu =0}^{n-1}F((x+\nu )/n)=n^{-s}F\left(x\right)$ (n ∈ ℕ) with s ∈ ℂ, investigated for instance by Artin (1931), Yoder (1975), Kubert (1979), and Milnor (1983), is extended to      $1/n{\sum }_{\nu =0}^{n-1}F((x+\nu )/n)={\sum }_{d=1}^{\infty }{\lambda }_n\left(d\right)F\left(dx\right)$ (n ∈ ℕ) with complex valued sequences ${\lambda }_n$. This leads to new results on the periodic integrable and the aperiodic continuous solutions F:ℝ₊ → ℂ interrelating the theory of functional equations and the theory of arithmetic functions.

For infinite discrete additive semigroups $X\subset [0,\infty )$ we study normed algebras of arithmetic functions $g:X\to ℂ$ endowed with the linear operations and the convolution. In particular, we investigate the problem of scaling the mean deviation of related multiplicative functions for $X=log\mathbb{N}$. This involves an extension of Banach algebras of arithmetic functions by introducing weight functions and proving a weighted inversion theorem of Wiener type in the frame of Gelfand’s theory of commutative Banach algebras.

In the earlier paper [Proc. Amer. Math. Soc. 135 (2007)], we studied solutions g: ℕ → ℂ to convolution equations of the form $a_d\ast g^{\ast d}+a_{d-1}\ast g^{\ast (d-1)}+\cdots +a₁\ast g+a₀=0$, where $a₀,...,a_d:\mathbb{N}\to ℂ$ are given arithmetic functions associated with Dirichlet series which converge on some right half plane, and also g is required to be such a function. In this article, we extend our previous results to multidimensional general Dirichlet series of the form ${\sum }_{x\in X}f\left(x\right)e^{-sx}$ ($s\in {ℂ}^k$), where $X\subseteq {[0,\infty )}^k$ is an additive subsemigroup. If X is discrete and a certain solvability criterion is satisfied,...

For each natural number $n$ we determine the average order $\alpha \left(n\right)$ of the elements in a cyclic group of order $n$. We show that more than half of the contribution to $\alpha \left(n\right)$ comes from the $\varphi \left(n\right)$ primitive elements of order $n$. It is therefore of interest to study also the function $\beta \left(n\right)=\alpha \left(n\right)/\varphi \left(n\right)$. We determine the mean behavior of $\alpha$, $\beta$, $1/\beta$, and also consider these functions in the multiplicative groups of finite fields.