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A189256
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Number of permutations p of 1,2,...,n satisfying |p(i+5)-p(i)|<>5 for all 1<=i<=n-5.
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5
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1, 2, 6, 24, 120, 672, 4128, 28992, 231936, 2088960, 20434944, 221871360, 2645370624, 34344038400, 482103767040, 7269498483456, 117240911729664, 2013265377314688, 36665783917283328, 705762463906133760, 14313891805008665856
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OFFSET
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1,2
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COMMENTS
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a(n) is also number of ways to place n nonattacking pieces rook + leaper[5,5] on an n X n chessboard.
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LINKS
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FORMULA
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Asymptotic (R. Tauraso 2006, quadratic term V. Kotesovec 2011): a(n)/n! ~ (1 + 16/n + 110/n^2)/e^2.
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CROSSREFS
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KEYWORD
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nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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