where s is a Sachs graph (as defined in 3 ) , Sn is the set of all Sachs graphs with n vertices, c(s) is the number of components3 and r(s) is the number of cycles 3, in S. N is the number of vertices in G. This formula may be applied to the graphs associated with conjugated hydrocarbons in a straightforward way, as described by Graovac et al.3. There have been several other (ostensibly differe...