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A189567
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Number of permutations p of 1,2,...,n satisfying |p(i+2)-p(i)|<>5 and |p(j+5)-p(j)|<>2 for all i=1..n-2, j=1..n-5.
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4
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1, 2, 6, 24, 120, 392, 1810, 10400, 72228, 589674, 5196870, 52398658, 588036216, 7274466172, 98024173852, 1427556373892
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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[2,5] on an n X n chessboard.
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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, A189563, A189564, A189565, A189566.
Sequence in context: A178010 A062348 A189856 * A189859 A189569 A174701
Adjacent sequences: A189564 A189565 A189566 * A189568 A189569 A189570
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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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