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A220509
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n^3 + 3n + 3^n.
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7
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1, 7, 23, 63, 157, 383, 963, 2551, 7097, 20439, 60079, 178511, 533205, 1596559, 4785755, 14352327, 43050865, 129145127, 387426375, 1162268383, 3486792461, 10460362527, 31381070323, 94143191063, 282429550377, 847288625143, 2541865845983, 7625597504751
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OFFSET
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0,2
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COMMENTS
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The subsequence of primes begins: 7, 23, 157, 383, 2551, see A220701 for the associated n.
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LINKS
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FORMULA
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G.f.: (1 - 8*x^2 + 6*x^3 - 11*x^4)/((1-x)^4*(1-3*x)). - Vincenzo Librandi, Dec 18 2012
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EXAMPLE
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a(1) = 1^3 + 3*1 + 3^1 = 7.
a(2) = 2^3 + 3*2 + 3^2 = 23.
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MATHEMATICA
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Table[n^3 + 3*n + 3^n, {n, 0, 30}] (* T. D. Noe, Dec 17 2012 *)
CoefficientList[Series[(1 - 8*x^2 + 6*x^3 - 11*x^4)/((1-x)^4*(1-3x)), {x, 0, 40}], x] (* Vincenzo Librandi, Dec 18 2012 *)
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PROG
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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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