Let n denote a positive integer. A graph Γ of diameter at least n is said to be n-distancebalanced whenever for any pair of vertices u, v of Γ at distance n, the number of vertices closer to u than to v is equal to the number of vertices closer to v than to u. In this article we consider n = 2 (e.g. we consider 2-distance-balanced graphs). We show that there exist 2-distance-balanced graphs that are not 1-distance-balanced (e.g. distance-balanced). We characterize all connected 2-distance-balanced graphs that are not 2-connected. We also characterize 2-distance-balanced graphs that can be obtained as cartesian product or lexicographic product of two graphs.Keywords: n-distance-balanced graph, cartesian product, lexicographic product.Math. Subj. Class.: 05C12, 05C76
Introductory remarksA graph Γ is distance-balanced if for each pair u, v of adjacent vertices of Γ the number of vertices closer to u than to v is equal to the number of vertices closer to v than to u. Although these graphs are interesting from the purely graph-theoretical point of view, they also have applications in other areas of research, such as mathematical chemistry and communication networks. It is for that reason that they have been studied from various different points of view in the literature.Distance-balanced graphs were first studied by Handa [9] in 1999. The name distancebalanced, however, was introduced nine years later by Jerebic, Klavžar and Rall [12]. The * We thank the two anonymous referees for many useful comments and suggestions that have greatly improved our initial manuscript, especially for pointing out the mistake in Theorem 5.4.