OFFSET
1,2
REFERENCES
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).
FORMULA
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(5), a(9), a(10) corrected and more terms from Sean A. Irvine, Nov 06 2017
STATUS
approved