A remark on the number of automorphisms of some algebraic structures

Abstract

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 evolution algebras, graphs, monoids, partial groups and posets.