OFFSET
1,2
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).
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
MATHEMATICA
CoefficientList[Series[162 x (2 + 9 x)/(1 - 9 x)^4, {x, 0, 30}], x] (* Vincenzo Librandi, Feb 12 2013 *)
PROG
(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
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Mohammad K. Azarian, Apr 30 2007
EXTENSIONS
Offset corrected by Mohammad K. Azarian, Nov 20 2008
STATUS
approved