A170831 a(n) = 2^(floor(n/2))+2^(floor(n/2)-1)-2^(floor((n-1)/3)).

2, 2, 4, 4, 10, 8, 20, 20, 40, 40, 88, 80, 176, 176, 352, 352, 736, 704, 1472, 1472, 2944, 2944, 6016, 5888, 12032, 12032, 24064, 24064, 48640, 48128, 97280, 97280, 194560, 194560, 391168, 389120, 782336, 782336, 1564672, 1564672, 3137536, 3129344, 6275072

Offset

2,1

Links

Table of n, a(n) for n=2..44.

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

Index entries for linear recurrences with constant coefficients, signature (0,2,2,0,-4).

Formula

a(n) = 2*a(n-2)+2*a(n-3)-4*a(n-5). G.f.: -2*x^2*(x^4+2*x^3-x-1) / ((2*x^2-1)*(2*x^3-1)). - Colin Barker, Jul 25 2013

Crossrefs

Cf. A170832, A170833, A170834.

Sequence in context: A318838 A231523 A114338 * A133406 A240381 A295746

Adjacent sequences: A170828 A170829 A170830 * A170832 A170833 A170834

Keyword

nonn,easy

Author

N. J. A. Sloane, Dec 30 2009

Status

approved