On the Tutte and Matching Polynomials for Complete Graphs

Abstract

Let T(G; X, Y) be the Tutte polynomial for graphs. We study the sequence ta,b(n) = T(Kn; a, b) where a, b are integers, and show that for every μ ∈ ℕ the sequence ta,b(n) is ultimately periodic modulo μ provided a ≠ 1 mod μ and b ≠ 1 mod μ. This result is related to a conjecture by A. Mani and R. Stones from 2016. The theorem is a consequence of a more general theorem which holds for a wide class of graph polynomials definable in Monadic Second Order Logic. This gives also similar results for the various substitution instances of the bivariate matching polynomial and the trivariate edge elimination polynomial ξ(G; X, Y, Z) introduced by I. Averbouch, B. Godlin and the second author in 2008. All our results depend on the Specker-Blatter Theorem from 1981, which studies modular recurrence relations of combinatorial sequences which count the number of labeled graphs.