OFFSET
0,5
COMMENTS
From R. J. Mathar, Apr 29 2019: (Start)
The numbers of labeled 2-regular digraphs with n >= 1 nodes and 1 <= k <= n components are
0;
0, 0;
1, 0, 0;
9, 0, 0, 0;
216, 0, 0, 0, 0;
7560, 10, 0, 0, 0, 0;
357120, 315, 0, 0, 0, 0, 0;
22025430, 14931, 0, 0, 0, 0, 0, 0;
1720751760, 879984, 280, 0, 0, 0, 0, 0, 0;
...
with row sums A007107. (End)
REFERENCES
R. W. Robinson, personal communication.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1982.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..253 (first 49 terms from R. W. Robinson)
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
STATUS
approved