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A319612
Number of regular simple graphs spanning n vertices.
14
1, 0, 1, 1, 7, 13, 171, 931, 45935, 1084413, 155862511, 10382960971, 6939278572095, 2203360500122299, 4186526756621772343, 3747344008241368443819, 35041787059691023579970847, 156277111373303386104606663421, 4142122641757598618318165240180095
OFFSET
0,5
COMMENTS
A graph is regular if all vertices have the same degree. The span of a graph is the union of its edges.
FORMULA
a(n) = A295193(n) - 1.
EXAMPLE
The a(4) = 7 edge-sets:
{{1,2},{3,4}}
{{1,3},{2,4}}
{{1,4},{2,3}}
{{1,2},{1,3},{2,4},{3,4}}
{{1,2},{1,4},{2,3},{3,4}}
{{1,3},{1,4},{2,3},{2,4}}
{{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}}
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 17 2018
EXTENSIONS
a(16)-a(18) from Andrew Howroyd, Sep 02 2019
STATUS
approved