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Search: id:A095818
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| A095818 |
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Number of permutations of 1..n with no five elements in correct or reverse order. |
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+0
3
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| 1, 2, 6, 24, 118, 714, 5012, 40164, 361872, 3621366, 39854930, 478427452, 6221137644, 87112280208, 1306869108686, 20912175669082, 355537064658852, 6400095163337508, 121608318630457872
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OFFSET
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1,2
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COMMENT
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For no n do either of the subsequences n(n+1)(n+2)(n+3)(n+4) or (n+4)(n+3)(n+2)(n+1)n occur in any permutation.
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LINKS
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Jackson, D. M. and Read, R. C., A note on permutations without runs of given length, Aequationes Math. 17 (1978), no. 2-3, 336-343.
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FORMULA
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G.f. for number of permutations of 1..n with no m elements in correct or reverse order is Sum(n!*((2*x^m-x^(m+1)-x)/(x^m-1))^n,n=0..infinity). - Ivana Jovovic ( ivana121(AT)EUnet.yu ), Nov 11 2007
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CROSSREFS
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Cf. A002464, A095816, A095817.
Sequence in context: A088713 A135106 A005394 this_sequence A052397 A047889 A094198
Adjacent sequences: A095815 A095816 A095817 this_sequence A095819 A095820 A095821
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KEYWORD
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nonn
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AUTHOR
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Jonas Wallgren (jonwa(AT)ida.liu.se), Jun 08 2004
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EXTENSIONS
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More terms from Ivana Jovovic ( ivana121(AT)EUnet.yu ), Nov 11 2007
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