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Search: id:A061990
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| A061990 |
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Number of ways to place 4 nonattacking queens on a 4 X n board. |
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+0
6
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| 0, 0, 0, 0, 2, 12, 46, 140, 344, 732, 1400, 2468, 4080, 6404, 9632, 13980, 19688, 27020, 36264, 47732, 61760, 78708, 98960, 122924, 151032, 183740, 221528, 264900, 314384, 370532, 433920, 505148, 584840, 673644, 772232, 881300
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OFFSET
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0,5
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LINKS
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V. Kotesovec, Ways of placing non-attacking queens and kings..., part of "Between chessboard and computer", 1996, pp. 204 - 206.
E. Lucas, Recreations mathematiques I, Albert Blanchard, Paris, 1992, p. 231.
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FORMULA
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G.f.: -2*x^4*(x^3-x^2+x+1)*(x^4+4*x^2+1)/(x-1)^5 Recurrence: a(n)=5*a(n-1)-10*a(n-2)+10*a(n-3)-5*a(n-4)+a(n-5), n >= 12. Explicit formula (H. Tarry, 1890): a(n)=n^4-18*n^3+139*n^2-534*n+840, n >= 7.
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CROSSREFS
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Cf. A061989.
Sequence in context: A066258 A123771 A046991 this_sequence A006742 A003993 A129018
Adjacent sequences: A061987 A061988 A061989 this_sequence A061991 A061992 A061993
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KEYWORD
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nonn
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AUTHOR
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Antonio G. Astudillo (afg_astudillo(AT)hotmail.com), May 29 2001
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