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A128961
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a(n) = (n^3 - n)*3^n.
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1
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0, 54, 648, 4860, 29160, 153090, 734832, 3306744, 14171760, 58458510, 233834040, 911952756, 3482001432, 13057505370, 48212327520, 175630621680, 632270238048, 2252462723046, 7949868434280, 27824539519980, 96653663595720
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OFFSET
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1,2
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (12,-54,108,-81).
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FORMULA
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G.f.: 54*x^2/(1-3*x)^4. - Vincenzo Librandi, Feb 12 2013
a(n) = 12*a(n-1)-54*a(n-2)+108*a(n-3)-81*a(n-4). - Vincenzo Librandi, Feb 12 2013
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MATHEMATICA
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LinearRecurrence[{12, -54, 108, -81}, {0, 54, 648, 4860}, 30] (* or *) CoefficientList[Series[54 x/(1 - 3 x)^4, {x, 0, 30}], x] (* Vincenzo Librandi, Feb 12 2013 *)
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PROG
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(MAGMA) [(n^3-n)*3^n: n in [1..25]]; /* or */ I:=[0, 54, 648, 4860]; [n le 4 select I[n] else 12*Self(n-1)-54*Self(n-2)+108*Self(n-3)-81*Self(n-4): n in [1..25]]; // Vincenzo Librandi, Feb 12 2013
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CROSSREFS
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Cf. A128796, A036289.
Sequence in context: A086577 A193152 A253006 * A218130 A321635 A090835
Adjacent sequences: A128958 A128959 A128960 * A128962 A128963 A128964
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KEYWORD
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nonn,easy
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AUTHOR
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Mohammad K. Azarian, Apr 28 2007
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EXTENSIONS
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Offset corrected by Mohammad K. Azarian, Nov 20 2008
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STATUS
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approved
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