We initiate the study of the twisted conjugacy growth series of a finitely generated group, the formal power series associated to the twisted conjugacy growth function. Our main result is that this series is always an N-rational function when the group in question is virtually abelian, and that this function can be explicitly computed from appropriate information about the group and the twisting endomorphism. We also show that the relative growth series of any twisted conjugacy class in a finitely generated virtually abelian group is itself an explicitly computable N-rational function.

This paper explores the nature of the solution sets of systems of equations in virtually abelian groups. We view this question from two angles. From a formal language perspective, we prove that the set of solutions to a system of equations forms an EDT0L language, with respect to a natural normal form. Looking at growth, we show that the growth series of the language of solutions is rational. Furthermore, considering the set of solutions as a set of tuples of group elements, we show that it has rational relative growth series with respect to any finite generating set.

This paper explores the nature of the solution sets of systems of equations in virtually abelian groups. We view this question from two angles. From a formal language perspective, we prove that the set of solutions to a system of equations forms an EDT0L language, with respect to a natural normal form. Looking at growth, we show that the growth series of the language of solutions is rational. Furthermore, considering the set of solutions as a set of tuples of group elements, we show that it has rational relative growth series with respect to any finite generating set.

We show that any subgroup of a finitely generated virtually abelian group G grows rationally relative to G, that the set of right cosets of any subgroup of G grows rationally, and that the set of conjugacy classes of G grows rationally. These results hold regardless of the choice of finite weighted generating set for G.