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A005642 Number of 2-diregular connected digraphs with n nodes.
(Formerly M2689)
2
1, 3, 7, 24, 117, 663, 4824, 40367, 381554, 4001849, 46043780, 576018785, 7783281188, 112953364381, 1752128923245, 28930230194371, 506596534953769 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Table of n, a(n) for n=2..18.

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)

CROSSREFS

Sequence in context: A135688 A252785 A229039 * A019055 A300515 A041045

Adjacent sequences:  A005639 A005640 A005641 * A005643 A005644 A005645

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified November 13 07:13 EST 2019. Contains 329085 sequences. (Running on oeis4.)