In these notes we look at the following question. Given a category $\mathcal C$ of algebraic structure (e.g. the category of groups, monoids, partial groups, ...) and a rational $r\in \mathbb Q$, does there exists an element $x\in \mathcal C$ such that the size of its automorphism group $\text{ Aut}_{ \mathcal C} (x)$ divided by the size of $x$ (whatever that would means) is equal to $r$\,? To our knowledge, this question was introduced by T\u{ a}rn\u{ a}uceanu in the category of groups. Here, we answer positively to this question in the categories of graphs, monoids, partial groups and posets.
Categories: math.GR