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A108305
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Number of set partitions of {1, ..., n} that avoid 4-crossings.
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2
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1, 1, 2, 5, 15, 52, 203, 877, 4139, 21119, 115495, 671969, 4132936, 26723063, 180775027, 1274056792, 9320514343, 70548979894, 550945607475, 4427978077331, 36544023687590
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| Sophie Burrill, Sergi Elizalde, Marni Mishna and Lily Yen, A generating tree approach to k-nonnesting partitions and permutations, Arxiv preprint arXiv:1108.5615, 2011
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LINKS
| M. Bousquet-Melou and G. Xin, On partitions avoiding 3-crossings, math.CO/0506551.
Chen, W., Deng, E., Du, R., Stanley, R. and Yan, C., Crossings and nestings of matchings and partitions, math.CO/0501230
Marni Mishna and Lily Yen, Set partitions with no k-nesting, Arxiv preprint arXiv:1106.5036, 2011
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EXAMPLE
| There are 4140 partitions of 8 elements, but a(8)=4139 because the partition (1,5)(2,6)(3,7)(4,8) has a 4-crossing
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CROSSREFS
| Sequence in context: A148092 A099262 A141081 * A099263 A192865 A164863
Adjacent sequences: A108302 A108303 A108304 * A108306 A108307 A108308
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KEYWORD
| easy,nonn
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AUTHOR
| Mireille Bousquet-Melou (bousquet(AT)labri.fr), Jun 29 2005
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