Coordination sequences for root lattices and related graphs

Abstract

The coordination sequence s _Λ(k) of a graph Λ counts the number of its vertices which have distance k from a given vertex, where the distance between two vertices is defined as the minimal number of bonds in any path connecting them. For a large class of graphs, including in particular the classical root lattices, we present the coordination sequences and their generating functions, summarizing and extending recent results of Conway and Sloane [1].