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A189563
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Number of permutations p of 1,2,...,n satisfying |p(i+1)-p(i)|<>4 and |p(j+4)-p(j)|<>1 for all i=1..n-1, j=1..n-4.
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8
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1, 2, 6, 24, 48, 182, 868, 5752, 37156, 296944, 2738820, 28894206, 335399468, 4285522402, 59536763892, 892785282788
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OFFSET
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1,2
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COMMENTS
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a(n) is also the number of ways to place n nonattacking pieces rook + leaper[1,4] on an n X n chessboard (in fairy chess the leaper[1,4] is called a giraffe).
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LINKS
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Table of n, a(n) for n=1..16.
V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech)
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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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Cf. A137774, A189358.
Sequence in context: A113904 A099144 A189851 * A104114 A175624 A118038
Adjacent sequences: A189560 A189561 A189562 * A189564 A189565 A189566
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KEYWORD
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nonn,hard
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AUTHOR
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Vaclav Kotesovec, Apr 23 2011
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STATUS
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approved
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