Complex valued multiplicative functions with bounded partial sums

Abstract

We present a class of multiplicative functions $f:\mathbb{N}\to \mathbb{C}$ with bounded partial sums. The novelty here is that our functions do not need to have modulus bounded by $1$. The key feature is that they pretend to be the constant function $1$ and that for some prime $q$, ${\sum }_{k=0}^{\infty }\frac{f(q^k)}{q^k}=0$. These combined with other conditions guarantee that these functions are periodic and have sum equal to zero inside each period. Further, we study the class of multiplicative functions $f=f_1\ast f_2$, where each $f_j$ is multiplicative and periodic with bounded partial sums. We show an omega bound for the partial sums ${\sum }_{n\le x}f(n)$ and an upper bound that is related with the error term in the classical Dirichlet divisor problem.

arXiv comment13 pages. To appear in Bull Braz Math Soc