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 A326251 Number of digraphs with vertices {1..n} whose increasing edges are not crossing. 5
 1, 2, 16, 512, 49152, 11534336, 6039797760, 6768868458496, 15885743998107648, 77083611222073409536, 767126299049285413502976, 15572324598183490228037091328, 642316330843573124053884695740416, 53681919993405760099480940765478125568 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 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. Conjecture: Also the number of non-nesting digraphs with vertices {1..n} whose increasing edges are not crossing, where two edges (a,b), (c,d) are nesting if a < c < d < b or c < a < b < d. LINKS FORMULA a(n) = 2^(n * (n + 1)/2) * A054726(n). MATHEMATICA croXQ[eds_]:=MatchQ[eds, {___, {x_, y_}, ___, {z_, t_}, ___}/; x

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Last modified November 30 21:20 EST 2021. Contains 349426 sequences. (Running on oeis4.)