

A326329


Number of simple graphs covering {1..n} with no crossing or nesting edges.


9



1, 0, 1, 4, 13, 44, 149, 504, 1705, 5768, 19513, 66012
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OFFSET

0,4


COMMENTS

Covering means there are no isolated vertices. Two edges {a,b}, {c,d} are crossing if a < c < b < d or c < a < d < b, and nesting if a < c < d < b or c < a < b < d.


LINKS



MATHEMATICA

Table[Length[Select[Subsets[Subsets[Range[n], {2}]], Union@@#==Range[n]&&!MatchQ[#, {___, {x_, y_}, ___, {z_, t_}, ___}/; x<z<y<tz<x<t<yx<z<t<yz<x<y<t]&]], {n, 0, 5}]


CROSSREFS

The case for set partitions is A001519.
Covering simple graphs are A006129.
The case with just nesting or just crossing edges forbidden is A324169.
The binomial transform is the noncovering case A326244.


KEYWORD

nonn,more


AUTHOR



STATUS

approved



