Let $A=\{a_n\}_{n=1}^\infty$ be a sequence of positive reals. In the spirit of the Erdös we say that $ E_A=\{ \sum_{n=1}^\infty \frac{1}{c_na_n}; c_n \mbox{is a positive integer}\}$ is an expressible set of the sequence $A$. We study certain properties of such kind of sets.
