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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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9
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1, 2, 2, 8, 20, 94, 438, 2766, 19480, 163058, 1546726, 16598282, 197708058, 2586423174, 36769177348, 563504645310, 9248221393974, 161670971937362, 2996936692836754
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| An empress moves like a rook and a knight
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LINKS
| V. Kotesovec, Number of ways of placing non-attacking queens and kings on boards of various sizes
W. Schubert, N-Queens page
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FORMULA
| Conjecture (Vaclav Kotesovec, 26.1.2011): 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 (proved)
a(n)/n! -> 1/e^4 for 0<r<s (conjectured)
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CROSSREFS
| Cf. A002464, A110128, A117574, A089222, A002493
Sequence in context: A080040 A060823 A178076 * A167532 A151377 A151407
Adjacent sequences: A137771 A137772 A137773 * A137775 A137776 A137777
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KEYWORD
| nonn,hard
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AUTHOR
| Vaclav Kotesovec (kotesovec(AT)chello.cz), Jan 27 2011
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EXTENSIONS
| Terms a(16)-a(17) from Vaclav Kotesovec (kotesovec(AT)chello.cz), Feb 06 2011
Terms a(18)-a(19) from Wolfram Schubert, Jul 24 2011
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