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A005642
Number of 2-diregular connected digraphs with n nodes.
(Formerly M2689)
4
1, 3, 7, 24, 117, 663, 4824, 40367, 381554, 4001849, 46043780, 576018785, 7783281188, 112953364381, 1752128923245, 28930230194371, 506596534953769
OFFSET
2,2
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
M. V. S. Ramanath & T. R. Walsh, Enumeration and generation of a class of regular digraphs, J. Graph Theory 11 (1987), no. 4, 471-479. (Annotated scanned copy)
R. J. Mathar, Illustrations
CROSSREFS
Cf. A005641 (not necess. connected), A306892 (multiarcs allowed). Labeled version is A123544.
Sequence in context: A135688 A252785 A229039 * A019055 A300515 A041045
KEYWORD
nonn
STATUS
approved