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A125548
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Number of j-sets in symmetric group S_n.
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0
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0, 1, 2, 4, 8, 16, 30, 56, 102, 186, 336, 606, 1088, 1954, 3502, 6278, 11246, 20148, 36086, 64640, 115774, 207374, 371430, 665298, 1191646, 2134454, 3823160, 6847974, 12265912, 21970470, 39353006, 70488334, 126257182, 226149314
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| For a permutation p=p_1 p_2...p_n in S_n and a positive integer i<= n, we can view p_1 p_2...p_i as an element of S_i by order-preserving relabeling. The j-set of p is the set of i's such that p_1 p_2...p_i is an involution in S_i.
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REFERENCES
| Dongsu Kim and Jang Soo Kim, The Initial Involution Patterns of Permutations, Electron. J. Combin., Vol. 14 (1) (2007), #R2.
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FORMULA
| Kim and Kim give a g.f.
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CROSSREFS
| Sequence in context: A046127 A075529 A005305 * A164229 A054668 A164225
Adjacent sequences: A125545 A125546 A125547 * A125549 A125550 A125551
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Jan 03 2007
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 03 2007
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