1,3
R. C. Read, On the enumeration of a class of plane multigraphs, Aequat. Math., 31 (1986), 47-63.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Sequence in context: A193659 A020023 A027836 * A106327 A009309 A075817
Adjacent sequences: A007166 A007167 A007168 * A007170 A007171 A007172
nonn
N. J. A. Sloane (njas(AT)research.att.com).
