  Let $a$ and $b$ be relatively prime positive integers. In this paper the
weighted sum $\sum_{n\in{\rm NR}(a,b)}\lambda^{n-1}n^m$ is given explicitly or
in terms of the Apostol-Bernoulli numbers, where $m$ is a nonnegative integer,
and ${\rm NR}(a,b)$ denotes the set of positive integers nonrepresentable in
terms of $a$ and $b$.
