A326252 - OEIS

A326252

Number of digraphs with vertices {1..n} whose increasing edges are crossing.

0, 0, 0, 0, 16384, 22020096, 62679678976, 556181084962816

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OFFSET

0,5

COMMENTS

A directed edge (a,b) is increasing if a < b. Two edges (a,b), (c,d) are crossing if a < c < b < d or c < a < d < b.

LINKS

FORMULA

a(n) = 2^(n * (n + 1)/2) * A326210(n).

MATHEMATICA

croXQ[eds_]:=MatchQ[eds, {___, {x_, y_}, ___, {z_, t_}, ___}/; x<z<y<t||z<x<t<y];

Table[Length[Select[Subsets[Tuples[Range[n], 2]], croXQ[#]&]], {n, 0, 4}]

CROSSREFS

Simple graphs whose edges are crossing are A326210.

Digraphs whose increasing edges are not crossing are A326251.

Digraphs whose edges are not crossing are A326237.

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Jun 30 2019

STATUS

approved