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A189565
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Number of permutations p of 1,2,...,n satisfying |p(i+2)-p(i)|<>3 and |p(j+3)-p(j)|<>2 for all i=1..n-2, j=1..n-3.
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6
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1, 1, 2, 6, 12, 36, 174, 708, 4334, 31424, 263732, 2503296, 26844578, 316692056, 4090634212, 57274447458, 863488976620
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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[2,3] on an n X n chessboard (in fairy chess the leaper [2,3] is called a zebra).
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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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