A128992 a(n) = (n^3 - n^2)*9^n.

0, 324, 13122, 314928, 5904900, 95659380, 1406192886, 19284931008, 251048476872, 3138105960900, 37971082126890, 447368385785904, 5154903899851212, 58290067175240628, 648557066098144350

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 (36,-486,2916,-6561).

Crossrefs

Cf. A128796, A036289.

Programs

Magma

[(n^3-n^2)*9^n: n in [1..25]]; /* or */ I:=[0,324,13122,314928]; [n le 4 select I[n] else 36*Self(n-1)-486*Self(n-2)+2916*Self(n-3)-6561*Self(n-4): n in [1..25]]; // Vincenzo Librandi, Feb 12 2013

Mathematica

CoefficientList[Series[162 x (2 + 9 x)/(1 - 9 x)^4, {x, 0, 30}], x] (* Vincenzo Librandi, Feb 12 2013 *)

Formula

G.f.: 162*x^2*(2+9*x)/(1-9*x)^4. - Vincenzo Librandi, Feb 12 2013

a(n) = 36*a(n-1)-486*a(n-2)+2916*a(n-3)-6561*a(n-4). - Vincenzo Librandi, Feb 12 2013

Extensions

Offset corrected by Mohammad K. Azarian, Nov 20 2008