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 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 (list; graph; refs; listen; history; text; internal format)
 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. Is this (apart from offsets) the same as A073717? - R. J. Mathar, Jul 04 2019 LINKS Table of n, a(n) for n=0..11. Eric Marberg, Crossings and nestings in colored set partitions, arXiv preprint arXiv:1203.5738 [math.CO], 2012. Gus Wiseman, The a(5) = 44 covering simple graphs with no crossing or nesting edges. MATHEMATICA Table[Length[Select[Subsets[Subsets[Range[n], {2}]], Union@@#==Range[n]&&!MatchQ[#, {___, {x_, y_}, ___, {z_, t_}, ___}/; x

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Last modified October 1 02:33 EDT 2023. Contains 365812 sequences. (Running on oeis4.)