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A322635
Number of regular graphs with loops on n labeled vertices.
7
2, 4, 4, 24, 78, 1908, 23368, 1961200, 75942758, 25703384940, 4184912454930, 4462909435830552, 2245354417775573206, 10567193418810168583576, 24001585002447984453495392, 348615956932626441906675011568, 2412972383955442904868321667433106, 162906453913051798826796439651249753404
OFFSET
1,1
COMMENTS
A graph is regular if all vertices have the same degree. A loop adds 2 to the degree of its vertex.
MATHEMATICA
Table[Sum[SeriesCoefficient[Product[1+Times@@x/@s, {s, Select[Tuples[Range[n], 2], OrderedQ]}], Sequence@@Table[{x[i], 0, k}, {i, n}]], {k, 0, 2n}], {n, 6}]
PROG
(PARI) for(n=1, 10, print1(A322635(n), ", ")) \\ See A295193 for script, Andrew Howroyd, Aug 28 2019
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 21 2018
EXTENSIONS
a(11)-a(18) from Andrew Howroyd, Aug 28 2019
STATUS
approved