Published online by Cambridge University Press: 02 May 2017
For any finite abelian group $G$ with
$|G|=m$ ,
$A\subseteq G$ and
$g\in G$ , let
$R_{A}(g)$ be the number of solutions of the equation
$g=a+b$ ,
$a,b\in A$ . Recently, Sándor and Yang [‘A lower bound of Ruzsa’s number related to the Erdős–Turán conjecture’, Preprint, 2016, arXiv:1612.08722v1] proved that, if
$m\geq 36$ and
$R_{A}(n)\geq 1$ for all
$n\in \mathbb{Z}_{m}$ , then there exists
$n\in \mathbb{Z}_{m}$ such that
$R_{A}(n)\geq 6$ . In this paper, for any finite abelian group
$G$ with
$|G|=m$ and
$A\subseteq G$ , we prove that (a) if the number of
$g\in G$ with
$R_{A}(g)=0$ does not exceed
$\frac{7}{32}m-\frac{1}{2}\sqrt{10m}-1$ , then there exists
$g\in G$ such that
$R_{A}(g)\geq 6$ ; (b) if
$1\leq R_{A}(g)\leq 6$ for all
$g\in G$ , then the number of
$g\in G$ with
$R_{A}(g)=6$ is more than
$\frac{7}{32}m-\frac{1}{2}\sqrt{10m}-1$ .
This work was supported by the National Natural Science Foundation of China, Grant No. 11371195, and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.