A133648 a(n) = 2*3^n + 3^(n-1) - (n+1).

5, 18, 59, 184, 561, 1694, 5095, 15300, 45917, 137770, 413331, 1240016, 3720073, 11160246, 33480767, 100442332, 301327029, 903981122, 2711943403, 8135830248, 24407490785, 73222472398, 219667417239, 659002251764, 1977006755341

Offset: 1

Author

Gary W. Adamson, Sep 19 2007

Keywords

• nonn
• easy

Examples

			a(3) = 2*3^3 + 3^2 - 4 = 2*27 + 9 - 4.
		

Links

• Index entries for linear recurrences with constant coefficients, signature (5,-7,3).

Crossrefs

Cf. A000244, A108765, A133649 (inverse binomial transform).

Programs

Maple

A133648:=n->2*3^n+3^(n-1)-(n+1): seq(A133648(n), n=1..40); # Wesley Ivan Hurt, Apr 18 2017

Mathematica

Table[2*3^n + 3^(n - 1) - (n + 1), {n, 1, 50}] (* Stefan Steinerberger, Sep 20 2007 *)

Formula

O.g.f.: -x*(5-7*x+4*x^2)/((-1+x)^2*(-1+3*x)). - R. J. Mathar, Jan 07 2008

a(n) = A108765(n-1) + A108765(n). - Klaus Purath, Apr 13 2020