Quotients of numerical semigroups generated by two numbers

TL;DR

This paper investigates the properties of quotients of numerical semigroups generated by two coprime numbers, providing formulas, algorithms, and insights into their invariants, type, and Wilf's property.

Contribution

It introduces formulas and algorithms for invariants of these semigroups and explores their type, embedding dimension, and Wilf's property, along with a reverse problem analysis.

Findings

Type is always less than the embedding dimension.

Algorithms with quadratic complexity for invariants.

Confirmed Wilf's property for these semigroups.

Abstract

In this article, we study the quotients of numerical semigroups, generated by two coprime positive numbers, named (a,b) over d. We give formulae for the usual invariants of these semigroups, expressed in terms of continued fraction expansions and Ostrowski-like numeration of some rationals, simply related to entries a, b, d. So, we obtain quadratic complexity algorithms to compute these invariants. As a consequence, we will prove that, for these numerical semigroups, the type is always lower than the embedding dimension and deduce Wilf's property. We also consider the '' reverse problem'' : given J, a finite set of integers, we obtain an expression of all possible triplets (a, b, d), such that J is the set of minimal generators of (a,b) over d.