A170832 a(n) = 3^(floor(n/2))+3^(floor(n/2)-1)-3^(floor((n-1)/3)).

3, 3, 9, 9, 33, 27, 99, 99, 297, 297, 945, 891, 2835, 2835, 8505, 8505, 26001, 25515, 78003, 78003, 234009, 234009, 706401, 702027, 2119203, 2119203, 6357609, 6357609, 19112193, 19072827, 57336579, 57336579, 172009737, 172009737, 516383505, 516029211, 1549150515

Offset

2,1

Links

Table of n, a(n) for n=2..38.

R. P. Stanley, Problem 11348, Amer. Math. Monthly, 117 (2010), 87-88.

Index entries for linear recurrences with constant coefficients, signature (0,3,3,0,-9).

Formula

a(n) = 3*a(n-2) +3*a(n-3) -9*a(n-5). G.f.: -3*x^2*(x^4+3*x^3-x-1) / ((3*x^2-1)*(3*x^3-1)). - Colin Barker, Jul 26 2013

Mathematica

LinearRecurrence[{0, 3, 3, 0, -9}, {3, 3, 9, 9, 33}, 40] (* Harvey P. Dale, Dec 18 2015 *)

Crossrefs

Cf. A170831, A170833, A170834.

Sequence in context: A146575 A373322 A100066 * A232281 A223743 A117783

Adjacent sequences: A170829 A170830 A170831 * A170833 A170834 A170835

Keyword

nonn,easy

Author

N. J. A. Sloane, Dec 30 2009

Status

approved