Resumen

REZA ASHRAFI, ALI  y  LOGHMAN, AMIR. PI INDEX OF SOME BENZENOID GRAPHS. J. Chil. Chem. Soc. [online]. 2006, vol.51, n.3, pp. 968-970. ISSN 0717-9707.  doi: 10.4067/S0717-97072006000300008.

The Padmakar-Ivan (PI) index of a graph G is defined as PI(G) = ∑[neu(e|G)+ n_ev(e|G)], where neu(e|G) is the number of edges of G lying closer to u than to v, n_ev(e|G) is the number of edges of G lying closer to v than to u and summation goes over all edges of G. In this paper, we first compute the PI index of a class of pericondensed benzenoid graphs consisting of n rows, n ≤ 3, of hexagons of various lengths. Finally, we prove that for any connected graph G with exactly m edges, PI(G) ≤ m(m-1) with equality if and only if G is an acyclic graph or a cycle of odd length

Palabras clave : Topological index; PI index; Benzenoid graph; molecular graph.