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A137774
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Number of ways to place n nonattacking empresses on an n X n board.
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13
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1, 2, 2, 8, 20, 94, 438, 2766, 19480, 163058, 1546726, 16598282, 197708058, 2586423174, 36769177348, 563504645310, 9248221393974, 161670971937362, 2996936692836754, 58689061747521430, 1210222434323163704, 26204614054454840842, 594313769819021397534, 14086979362268860896282
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OFFSET
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1,2
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COMMENTS
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An empress moves like a rook and a knight.
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LINKS
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FORMULA
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Asymptotics (Vaclav Kotesovec, Jan 26 2011): a(n)/n! -> 1/e^4.
General asymptotic formulas for number of ways to place n nonattacking pieces rook + leaper[r,s] on an n X n board:
a(n)/n! -> 1/e^2 for 0<r=s
a(n)/n! -> 1/e^4 for 0<r<s
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CROSSREFS
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KEYWORD
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nonn,nice,hard
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AUTHOR
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EXTENSIONS
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Terms a(18)-a(19) from Wolfram Schubert, Jul 24 2011
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STATUS
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approved
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