A128801 a(n) = n*(n-1)*7^n.
0, 98, 2058, 28812, 336140, 3529470, 34588806, 322828856, 2905459704, 25422772410, 217505941730, 1827049910532, 15114685623492, 123436599258518, 996987917088030, 7975903336704240, 63275499804520304, 498294560960597394
Offset: 1
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
- Index entries for linear recurrences with constant coefficients, signature (21,-147,343).
Programs
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Magma
[(n^2-n)*7^n: n in [1..25]] // Vincenzo Librandi, Feb 12 2013
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Maple
g:=98*x^2/(1-7*x)^3: gser:=series(g,x=0,22): seq(coeff(gser,x,n),n=1..18); # Emeric Deutsch, May 04 2007
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Mathematica
LinearRecurrence[{21, -147, 343}, {0, 98, 2058}, 30] (* Vincenzo Librandi, Feb 12 2013 *)
Formula
G.f.: 98*x^2/(1-7*x)^3. - Emeric Deutsch, May 04 2007
a(n) = 21*a(n-1) - 147*a(n-2) + 343*a(n-3). - Vincenzo Librandi, Feb 12 2013
a(n) = 98*A027474(n). - R. J. Mathar, Apr 26 2015