An infinite family of graphs with Šoltés fraction uniformly above one half

Abstract

The Wiener index $W(G)$ of a connected graph $G$ is the sum of the distances between all unordered pairs of vertices. A vertex $x$ is a Šoltés vertex if $G-x$ is connected and $W(G-x)=W(G)$. We construct an infinite family of graphs in which the proportion of Šoltés vertices is strictly greater than $(\sqrt{21}-3)/3=0.5275\ldots>1/2$ and decreases to this value from $2/3$. The family is also described by a generalized Pell equation and starts from a $12$-vertex example of Akhmejanova et al. (Discrete Appl. Math. 325 (2023) 37-42). We also show that the construction remains valid after adding edges among certain vertices.