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A172207
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Number of ways to place 3 nonattacking bishops on a 3 X n board.
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4
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1, 6, 26, 86, 211, 426, 758, 1234, 1881, 2726, 3796, 5118, 6719, 8626, 10866, 13466, 16453, 19854, 23696, 28006, 32811, 38138, 44014, 50466, 57521, 65206, 73548, 82574, 92311, 102786, 114026, 126058, 138909, 152606, 167176, 182646, 199043, 216394, 234726, 254066
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = (9n^3 - 45n^2 + 106n - 108)/2, n>=4.
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MATHEMATICA
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CoefficientList[Series[(2 x^6 + 14 x^3 + 8 x^2 + 2 x + 1) / (x - 1)^4, {x, 0, 50}], x] (* Vincenzo Librandi, May 27 2013 *)
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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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