A174132 a(n) = 2*3^(n-1)-(-1)^n.

3, 5, 19, 53, 163, 485, 1459, 4373, 13123, 39365, 118099, 354293, 1062883, 3188645, 9565939, 28697813, 86093443, 258280325, 774840979, 2324522933, 6973568803, 20920706405, 62762119219, 188286357653, 564859072963

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..200

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

Formula

From Bruno Berselli, Jan 28 2011 - Jan 30 2011: (Start)

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

a(n) = A062547(A042963(n-1)).

a(n) = 2*sum[a(i), i=1..n-1]-2*(-1)^n+1 for n>1. (End)

Mathematica

Table[(2 3^(n-1) - (-1)^n), {n, 30}] (* Vincenzo Librandi, Aug 21 2014 *)
(* Alternative: *)
CoefficientList[Series[(3 - x)/((1 + x)(1 - 3 x)), {x, 0, 30}], x] (* Vincenzo Librandi, Aug 21 2014 *)

Prog

(Magma) [2*3^(n-1)-(-1)^n: n in [1..30]]; // Vincenzo Librandi, Aug 21 2014

Crossrefs

Cf. A154992.

Sequence in context: A148547 A360086 A127998 * A106918 A182357 A181519

Adjacent sequences: A174129 A174130 A174131 * A174133 A174134 A174135

Keyword

nonn,easy

Author

Vincenzo Librandi, Jan 27 2011

Status

approved