A connection between the poles of the zeta function of a recurrence sequence and the module of relations of its roots

Answering a question left open in previous research, we study the enumeration of poles of the zeta function $\phi (s)$ associated to an integer linear recurrence sequence $\{a_n\}$. This enumeration can count poles more than once, and we prove that this happens if and only if the module of relations of the roots of the recurrence is nontrivial. A review of the existing literature on the module of relations yields a series of sufficient conditions for the enumeration of poles of $\phi (s)$ to be injective. All of this is illustrated by examples of both cases.