The constant-isomer series are studied in relation to the periodic table of benzenoid hydrocarbons. General properties of the table are formulated in terms of explicit expressions. In particular a general expression for the formulas (CnHs) of the ground forms of the constant-isomer series was achieved. The numbers of the isomers (cardinalities of CnHs) are divided into to parts. Explicit equations are given for the first part of the cardinalities.