A128990 a(n) = (n^3 - n^2)*7^n.

0, 196, 6174, 115248, 1680700, 21176820, 242121642, 2582630848, 26149137336, 254227724100, 2392565359030, 21924598926384, 196490913105396, 1728112389619252, 14954818756320450, 127614453387267840

Offset: 1

Author

Mohammad K. Azarian, Apr 30 2007

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000
• Index entries for linear recurrences with constant coefficients, signature (28, -294, 1372, -2401).

Crossrefs

Cf. A128796, A036289.

Programs

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

Mathematica

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 *)

Formula

G.f.: 98*x^2*(2+7*x)/(1-7*x)^4. - Vincenzo Librandi, Feb 12 2013

a(n) = 28*a(n-1)-294*a(n-2)+1372*a(n-3)-2401*a(n-4). - Vincenzo Librandi, Feb 12 2013

Extensions

Offset corrected by Mohammad K. Azarian, Nov 20 2008