Published online by Cambridge University Press: 28 June 2013
For a given integer $n$ and a set
$ \mathcal{S} \subseteq \mathbb{N} $, denote by
${ R}_{h, \mathcal{S} }^{(1)} (n)$ the number of solutions of the equation
$n= {s}_{{i}_{1} } + \cdots + {s}_{{i}_{h} } $,
${s}_{{i}_{j} } \in \mathcal{S} $,
$j= 1, \ldots , h$. In this paper we determine all pairs
$( \mathcal{A} , \mathcal{B} )$,
$ \mathcal{A} , \mathcal{B} \subseteq \mathbb{N} $, for which
${ R}_{3, \mathcal{A} }^{(1)} (n)= { R}_{3, \mathcal{B} }^{(1)} (n)$ from a certain point on. We discuss some related problems.