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A032124
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"BIK" (reversible, indistinct, unlabeled) transform of 2,2,2,2...
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1
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2, 5, 12, 33, 90, 261, 756, 2241, 6642, 19845, 59292, 177633, 532170, 1595781, 4785156, 14353281, 43053282, 129153285, 387440172, 1162300833, 3486843450, 10460471301, 31381236756, 94143533121, 282430067922, 847289672325, 2541867422652, 7625600673633
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = (1/6)*((5-(-1)^n)*3^floor(n/2) + 2*3^n). - Ralf Stephan, May 11 2004
a(n) = 3*a(n-1)+3*a(n-2)-9*a(n-3). G.f.: -x*(9*x^2+x-2) / ((3*x-1)*(3*x^2-1)). - Colin Barker, Dec 15 2012
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MATHEMATICA
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CoefficientList[Series[-(9 x^2 + x - 2)/((3 x - 1) (3 x^2 - 1)), {x, 0, 30}], x] (* Vincenzo Librandi, Oct 19 2013 *)
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PROG
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(Magma) [(1/6)*((5-(-1)^n)*3^Floor(n/2) + 2*3^n): n in [1..30]]; // Vincenzo Librandi, Oct 19 2013
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CROSSREFS
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KEYWORD
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nonn,easy,changed
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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