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A189568
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Number of permutations p of 1,2,...,n satisfying |p(i+3)-p(i)|<>4 and |p(j+4)-p(j)|<>3 for all i=1..n-3, j=1..n-4.
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3
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1, 1, 2, 6, 24, 80, 326, 1566, 9544, 65036, 518498, 4750006, 48830634, 554929274, 6926227324, 93970452970, 1377573324202
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OFFSET
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0,3
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COMMENTS
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a(n) is also the number of ways to place n nonattacking pieces rook + leaper[3,4] on an n X n chessboard.
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LINKS
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FORMULA
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Asymptotic: a(n)/n! ~ 1/e^4.
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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STATUS
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approved
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