  During his work devoted to Coxeter's friezes, M. Cuntz initiated the study of
the notion of $\lambda$-quiddity and raised the problem of the study of this
over some subsets of $\mathbb{C}$. The objective of this text is to bring some
new elements of response in the case of some cyclic subgroups of
($\mathbb{C},+$) generated by an algebraic number. In particular, we will study
the cases of subgroups generated by $a+b\sqrt{k}$.
