Nanotubes: Number of Kekulé Structures and Aromaticity. - István Lukovits; Ante Graovac; Erika Kálmán; György Kaptay; Peter I. Nagy; Sonja Nikolic; Jaroslav Sytchev; Nenad Trinajstic (J. Chem. Inf. Comput. Sci., 2003)