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A350912
Triangle read by rows: T(n,k) is the number of oriented graphs on n unlabeled nodes whose underlying graph is k-regular, k = 0..n-1.
4
1, 1, 1, 1, 0, 2, 1, 1, 4, 4, 1, 0, 4, 0, 12, 1, 1, 12, 62, 112, 56, 1, 0, 18, 0, 1602, 0, 456, 1, 1, 40, 2062, 32263, 92980, 46791, 6880, 1, 0, 68, 0, 748576, 0, 11210264, 0, 191536, 1, 1, 140, 103827, 19349672, 616991524, 3319462470, 2729098064, 292115960, 9733056
OFFSET
1,6
COMMENTS
The sum of the in-degree and out-degree at each node is k.
a(2*n,2*n-2) is the number of orientations (up to isomorphism) of the n-cocktail party graph. - Pontus von Brömssen, Apr 03 2022
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..253 (rows 1..22)
EXAMPLE
Triangle begins:
1;
1, 1;
1, 0, 2;
1, 1, 4, 4;
1, 0, 4, 0, 12;
1, 1, 12, 62, 112, 56;
1, 0, 18, 0, 1602, 0, 456;
...
CROSSREFS
Row sums are A350913.
Main diagonal is A000568.
The labeled version is A351263.
Cf. A051031 (graphs), A350910 (digraphs).
Sequence in context: A245596 A326611 A083293 * A055370 A350021 A176388
KEYWORD
nonn,tabl
AUTHOR
Andrew Howroyd, Jan 29 2022
STATUS
approved