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: A050637 A020023 A027836 this_sequence A106327 A009309 A075817

Adjacent sequences: A007166 A007167 A007168 this_sequence A007170 A007171 A007172

nonn

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