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A266278
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Number of legal Go positions on a 2 X n board.
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6
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5, 57, 489, 4125, 35117, 299681, 2557605, 21826045, 186255781, 1589441093, 13563736693, 115748216413, 987755062201, 8429158472781, 71931509371765, 613838505628281, 5238284505542721, 44701699729693429, 381468772192258129, 3255321946095461785, 27779786302899765081
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OFFSET
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1,1
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LINKS
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J. Tromp and G. Farnebäck, Combinatorics of Go, Lecture Notes in Computer Science, 4630, 84-99, 2007.
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FORMULA
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a(n) = 10*a(n-1)-16*a(n-2)+31*a(n-3)-13*a(n-4)+20*a(n-5)+2*a(n-6)-a(n-7).
G.f.: x*(1 + x)^2*(5 - 3*x - 5*x^3 - x^4) / ((1 + x^2)*(1 - 10*x + 15*x^2 - 21*x^3 - 2*x^4 + x^5)). - Colin Barker, Jan 05 2018
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EXAMPLE
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For n = 1, the a(1) = 5 legal 2 X 1 boards are .. X. O. .X .O
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PROG
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(PARI) Vec(x*(1 + x)^2*(5 - 3*x - 5*x^3 - x^4) / ((1 + x^2)*(1 - 10*x + 15*x^2 - 21*x^3 - 2*x^4 + x^5)) + O(x^40)) \\ Colin Barker, Jan 05 2018
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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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EXTENSIONS
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STATUS
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approved
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