Journal of Integer Sequences, Vol. 25 (2022), Article 22.2.4

Directed Graphs from Exact Covering Systems


Dana Neidmann
Department of Mathematics
University of Illinois at Urbana-Champaign
Urbana, IL 61801
USA

Abstract:

Given an exact covering system S = {ai (mod di) : 1 ≤ i ≤ r}, we introduce the corresponding exact covering system digraph (ECSD) GS = G(d1n+a1, ..., drn+ar). The vertices of GS are the integers and the edges are (n, din + ai) for each n ∈ Z and for each congruence in the covering system. We study the structure of these directed graphs, which have finitely many components, one cycle per component, as well as indegree 1 and outdegree r at each vertex. We also explore the link between ECSDs that have a single component and non-standard digital representations of integers.


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(Concerned with sequences A002487 A110081.)


Received March 2 2021; revised versions received November 3 2021; January 24 2022; January 31 2022. Published in Journal of Integer Sequences, February 1 2022.


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