The edge-Hosoya polynomial of benzenoid chains

The Hosoya polynomial is a well known vertex-distance based polynomial, closely correlated to the Wiener index and the hyper-Wiener index, which are widely used molecular-structure descriptors. In the present paper we consider the edge version of the Hosoya polynomial. For a connected graph $G$ let $d_e(G,k)$ be the number of (unordered) edge pairs at distance $k$. Then the edge-Hosoya polynomial of $G$ is $H_e(G,x) = \sum_{k \geq 0} d(G,k)x^k$. We investigate the edge-Hosoya polynomial of important chemical graphs known as benzenoid chains and derive the recurrence relations for them. These recurrences are then solved for linear benzenoid chains, which are also called polyacenes.