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A171590
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a(n) = 1+4^(n+1)-4*(-2)^n.
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1
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1, 25, 49, 289, 961, 4225, 16129, 66049, 261121, 1050625, 4190209, 16785409, 67092481, 268468225, 1073676289, 4295098369, 17179607041, 68720001025, 274876858369, 1099513724929, 4398042316801, 17592194433025, 70368727400449
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: (1+22*x-32*x^2)/((x-1)*(2*x+1)*(4*x-1)).
a(n) = 3*a(n-1)+6*a(n-2)-8*a(n-3).
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MATHEMATICA
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CoefficientList[Series[(1 + 22*x - 32*x^2)/((x - 1)*(2*x + 1)*(4*x-1)), {x, 0, 40}], x] (* Vincenzo Librandi, Dec 19 2012 *)
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PROG
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(Magma) I:=[1, 25, 49]; [n le 3 select I[n] else 3*Self(n-1) + 6*Self(n-2) - 8*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Dec 19 2012
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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