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A322659 Number of connected regular simple graphs on n labeled vertices. 4
1, 1, 1, 4, 13, 146, 826, 44808, 1074557, 155741296, 10381741786, 6939251270348, 2203360264480750, 4186526735251514044, 3747344007864300197810, 35041787059621536192399824, 156277111373298355107598128061, 4142122641757597729416733678931968 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
COMMENTS
A graph is regular if all vertices have the same degree.
LINKS
MATHEMATICA
csm[s_]:=With[{c=Select[Tuples[Range[Length[s]], 2], And[OrderedQ[#], UnsameQ@@#, Length[Intersection@@s[[#]]]>0]&]}, If[c=={}, s, csm[Sort[Append[Delete[s, List/@c[[1]]], Union@@s[[c[[1]]]]]]]]];
Table[If[n==1, 1, Length[Select[Subsets[Subsets[Range[n], {2}]], And[Union@@#==Range[n], SameQ@@Length/@Split[Sort[Join@@#]], Length[csm[#]]==1]&]]], {n, 6}]
CROSSREFS
Row sums of A324163.
Sequence in context: A067634 A203215 A198159 * A042537 A220038 A132512
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 22 2018
EXTENSIONS
a(8)-a(15) from Andrew Howroyd, Dec 23 2018
a(16)-a(18) from Andrew Howroyd, Sep 02 2019
STATUS
approved

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Last modified May 26 20:04 EDT 2024. Contains 372844 sequences. (Running on oeis4.)