

A003286


Number of semiregular digraphs (with loops) on n unlabeled nodes with each node having outdegree 2.
(Formerly M4441)


3



1, 7, 66, 916, 16816, 373630, 9727010, 289374391, 9677492899, 359305262944, 14663732271505, 652463078546373, 31435363120551013, 1630394318463367718, 90570555840053284171, 5365261686125108336540, 337616338011820295406352, 22490263897737210321234701, 1581153614004788257326876764
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OFFSET

2,2


COMMENTS

The directed graphs in this sequence need not be connected, but each node must have outdegree 2.  Sean A. Irvine, Apr 09 2015


REFERENCES

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


LINKS

Andrew Howroyd, Table of n, a(n) for n = 2..50
S. A. Choudum, K. R. Parthasarathy, Semiregular relations and digraphs, Nederl. Akad. Wetensch. Proc. Ser. A. {75}=Indag. Math. 34 (1972), 326334.
Steve Huntsman, Generalizing cyclomatic complexity via path homology, arXiv:2003.00944 [cs.SE], 2020.
Sean A. Irvine, Illustration of A003286(3).


CROSSREFS

Column k=2 of A259471.
Cf. A129524.
Sequence in context: A185181 A024395 A215077 * A244602 A223889 A197744
Adjacent sequences: A003283 A003284 A003285 * A003287 A003288 A003289


KEYWORD

nonn,nice


AUTHOR

N. J. A. Sloane


EXTENSIONS

a(7)a(9) from Sean A. Irvine, Apr 11 2015
Terms a(10) and beyond from Andrew Howroyd, Sep 13 2020


STATUS

approved



