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A143769
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Expansion of 3*x*(3*x+1)*(2*x-1) / ( (1+x)*(3*x^2+1) ).
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1
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-3, 0, 27, -18, -63, 36, 207, -126, -603, 360, 1827, -1098, -5463, 3276, 16407, -9846, -49203, 29520, 147627, -88578, -442863, 265716, 1328607, -797166, -3985803, 2391480, 11957427, -7174458, -35872263, 21523356, 107616807, -64570086, -322850403, 193710240
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OFFSET
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1,1
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COMMENTS
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All entries are multiples of 3.
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LINKS
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FORMULA
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a(n) = (3/2) * ((2*(-1)^n - 3) * (-3)^floor(n/2) - 3*(-1)^n ). - Ralf Stephan, Aug 17 2013
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MATHEMATICA
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CoefficientList[Series[3 (3 x + 1) (2 x - 1) / ((1 + x) (3 x^2 + 1)), {x, 0, 40}], x] (* Vincenzo Librandi, Aug 17 2013 *)
LinearRecurrence[{-1, -3, -3}, {-3, 0, 27}, 40] (* Harvey P. Dale, Dec 26 2014 *)
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PROG
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(PARI) a(n)=3/2*((2*(-1)^n-3)*(-3)^floor(n/2)-3*(-1)^n); \\ Ralf Stephan, Aug 17 2013
(Magma) I:=[-3, 0, 27]; [n le 3 select I[n] else -Self(n-1)-3*Self(n-2) -3*Self(n-3): n in [1..50]]; // Vincenzo Librandi, Aug 17 2013
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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STATUS
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approved
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