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A173963
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Number of nonoverlapping placements of one 1 X 1 square and one 2 X 2 square on an n X n board.
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2
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0, 0, 20, 108, 336, 800, 1620, 2940, 4928, 7776, 11700, 16940, 23760, 32448, 43316, 56700, 72960, 92480, 115668, 142956, 174800, 211680, 254100, 302588, 357696, 420000, 490100, 568620, 656208, 753536, 861300, 980220, 1111040, 1254528
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OFFSET
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1,3
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COMMENTS
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Also the number of placements of a horizontal and a vertical domino on the n X n board. - Ralf Stephan, Jun 10 2014
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LINKS
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FORMULA
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a(n) = (n^2 - 4) * (n-1)^2.
a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5), with a(1)=0, a(2)=0, a(3)=20, a(4)=108, a(5)=336. - Harvey P. Dale, Aug 16 2011
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MATHEMATICA
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Table[(n^2-4)(n-1)^2, {n, 40}] (* or *) LinearRecurrence[{5, -10, 10, -5, 1}, {0, 0, 20, 108, 336}, 40] (* Harvey P. Dale, Aug 16 2011 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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