OFFSET
1,3
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
R. C. Read, On the enumeration of a class of plane multigraphs, Aequat. Math. 31 (1986) no 1, 47-63.
FORMULA
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(9) corrected and more terms from Sean A. Irvine, Nov 07 2017
STATUS
approved