A128986 a(n) = (n^3 - n^2)*3^n.

0, 36, 486, 3888, 24300, 131220, 642978, 2939328, 12754584, 53144100, 214347870, 841802544, 3233287044, 12187005012, 45199057050, 165299408640, 597144113712, 2133912053412, 7552375012566, 26499561447600, 92260315250460

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 (12,-54,108,-81).

Crossrefs

Cf. A128796, A036289.

Programs

Magma

[(n^3 - n^2)*3^n: n in [1..25]]; // Vincenzo Librandi, Feb 11 2013

Mathematica

LinearRecurrence[{12, -54, 108, -81}, {0, 36, 486, 3888}, 30] (* Vincenzo Librandi, Feb 11 2013 *)

Formula

G.f.: 18x^2(2+3x)/(1-3x)^4. - R. J. Mathar, Dec 19 2008

a(n) = 12*a(n-1) - 54*a(n-2) + 108*a(n-3) - 81*a(n-4). - Vincenzo Librandi, Feb 11 2013

Extensions

Offset corrected by Mohammad K. Azarian, Nov 20 2008