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A128990
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a(n) = (n^3 - n^2)*7^n.
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1
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0, 196, 6174, 115248, 1680700, 21176820, 242121642, 2582630848, 26149137336, 254227724100, 2392565359030, 21924598926384, 196490913105396, 1728112389619252, 14954818756320450, 127614453387267840
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = 28*a(n-1)-294*a(n-2)+1372*a(n-3)-2401*a(n-4). - Vincenzo Librandi, Feb 12 2013
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MATHEMATICA
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CoefficientList[Series[98 x (2 + 7 x)/(1 - 7 x)^4, {x, 0, 30}], x] (* Vincenzo Librandi, Feb 12 2013 *)
LinearRecurrence[{28, -294, 1372, -2401}, {0, 196, 6174, 115248}, 20] (* Harvey P. Dale, Mar 04 2015 *)
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PROG
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(Magma) [(n^3-n^2)*7^n: n in [1..25]]; /* or */ I:=[0, 196, 6174, 115248]; [n le 4 select I[n] else 28*Self(n-1)-294*Self(n-2)+1372*Self(n-3)-2401*Self(n-4): n in [1..25]]; // Vincenzo Librandi, Feb 12 2013
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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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