J. Integer Seq. 3(2), Art. 00.2.2, electronic only (2000)
Summary
Summary: We propose and discuss several simple ways of obtaining new enumerative sequences from existing ones. For instance, the number of graphs considered up to the action of an involutory transformation is expressible as the semi-sum of the total number of such graphs and the number of graphs invariant under the involution. Another, less familiar idea concerns even- and odd-edged graphs: the difference between their numbers often proves to be a very simple quantity (such as n!). More than 30 new sequences will be constructed by these methods.
