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Search: id:A108305
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| A108305 |
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Number of set partitions of {1, ..., n} that avoid 4-crossings. |
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1
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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; listen)
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OFFSET
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0,3
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LINKS
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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
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EXAMPLE
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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
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Sequence in context: A108304 A056273 A099262 this_sequence A099263 A000110 A134381
Adjacent sequences: A108302 A108303 A108304 this_sequence A108306 A108307 A108308
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KEYWORD
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easy,nonn
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AUTHOR
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Mireille Bousquet-Melou (bousquet(AT)labri.fr), Jun 29 2005
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