A089143 a(n) = 9*2^n - 6.

3, 12, 30, 66, 138, 282, 570, 1146, 2298, 4602, 9210, 18426, 36858, 73722, 147450, 294906, 589818, 1179642, 2359290, 4718586, 9437178, 18874362, 37748730, 75497466, 150994938, 301989882, 603979770, 1207959546, 2415919098, 4831838202, 9663676410, 19327352826

Offset: 0

Author

Parthasarathy Nambi, Sep 21 2004

Keywords

• nonn
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (3,-2).

Crossrefs

Cf. A033484.

Programs

Mathematica

a=3; lst={a}; k=9; Do[a+=k; AppendTo[lst, a]; k+=k, {n, 0, 5!}]; lst (* Vladimir Joseph Stephan Orlovsky, Dec 16 2008 *)
9*2^Range[0,40]-6 (* Harvey P. Dale, Sep 15 2013 *)

PARI

my(x='x+O('x^32)); Vec(3*(1+x)/(1-3*x+2*x^2)) \\ Elmo R. Oliveira, May 24 2025

Formula

a(n) = 3*A033484(n).

From Elmo R. Oliveira, May 24 2025: (Start)

G.f.: 3*(x+1)/((x-1)*(2*x-1)).

E.g.f.: 3*exp(x)*(3*exp(x) - 2).

a(n) = 3*a(n-1) - 2*a(n-2). (End)