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A108305
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Number of set partitions of {1, ..., n} that avoid 4-crossings.
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3
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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
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OFFSET
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0,3
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LINKS
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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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KEYWORD
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easy,nonn,more
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AUTHOR
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STATUS
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approved
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