Bicyclic graphs with the smallest and largest numbers of connected sets

Abstract

For a graph $G$ with vertex set $V$, let N($G$) denote the number of nonempty subsets of $V$ that induce a connected graph in $G$. In this paper, we focus on determining N($G$) for $G$ in the family ${\mathbb{B}}_n$ of $n$-vertex bicyclic graphs. We find in ${\mathbb{B}}_n$ the structures of those graphs that possess the smallest, the largest, as well as the second-largest values of N($G$). Moreover, we compute the extreme values of N($G$) over ${\mathbb{B}}_n$.

15 pages, 9 figures