login
A005641
Number of 2-diregular digraphs with n nodes.
(Formerly M2757)
3
1, 3, 8, 27, 131, 711, 5055, 41607, 389759, 4065605, 46612528, 581713045, 7846380548, 113718755478, 1762208816647, 29073392136390, 508777045979418
OFFSET
2,2
COMMENTS
These graphs may have loops, whereas A219889 does not admit them. Both sequences do not admit multiedges. - R. J. Mathar, Mar 27 2019
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Richard J. Mathar, 2-regular Digraphs of the Lovelock Lagrangian, arXiv:1903.12477 [math.GM], 2019.
M. V. S. Ramanath and 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
Cf. A005642 (inverse Euler transform, connected graphs).
Sequence in context: A294197 A030495 A074271 * A377387 A260961 A230822
KEYWORD
nonn
STATUS
approved