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A055988
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Sequence is its own 4th difference.
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6
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1, 2, 7, 26, 95, 345, 1252, 4544, 16493, 59864, 217286, 788674, 2862617, 10390321, 37713313, 136886433, 496850954, 1803399103, 6545722210, 23758733815, 86236081273, 313007493212, 1136110191472, 4123691589365, 14967590689568
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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G.f.: (1-x)^3/(1 - 5x + 6x^2 - 4x^3 + x^4);
a(n) = Sum_{k=0..n} binomial(n+3k, 4k). (End)
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MATHEMATICA
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CoefficientList[Series[(1-x)^3/(1-5x+6x^2-4x^3+x^4), {x, 0, 40}], x] (* Vincenzo Librandi, Apr 05 2012 *)
LinearRecurrence[{5, -6, 4, -1}, {1, 2, 7, 26}, 30] (* Harvey P. Dale, Jan 15 2017 *)
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PROG
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(Magma) I:=[1, 2, 7, 26]; [n le 4 select I[n] else 5*Self(n-1)-6*Self(n-2)+4*Self(n-3)-Self(n-4): n in [1..30]]; // Vincenzo Librandi, Apr 05 2012
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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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