1,3

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

R. C. Read, On the enumeration of a class of plane multigraphs, Aequat. Math., 31 (1986), 47-63.

Sequence in context: A009693 A104190 A152661 this_sequence A136722 A085615 A054726

Adjacent sequences: A007167 A007168 A007169 this_sequence A007171 A007172 A007173

nonn

N. J. A. Sloane (njas(AT)research.att.com).