login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A128205 a(n) = 2^(n-1)*A047240(n). 1
0, 1, 4, 24, 56, 128, 384, 832, 1792, 4608, 9728, 20480, 49152, 102400, 212992, 491520, 1015808, 2097152, 4718592, 9699328, 19922944, 44040192, 90177536, 184549376, 402653184, 822083584, 1677721600, 3623878656, 7381975040, 15032385536, 32212254720 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

-a(n) is the Hankel transform of A030662(n) = binomial(2*n,n)-1.

LINKS

Colin Barker, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (2,0,8,-16).

FORMULA

a(n) = 2^(n-1)*(cos(2*Pi*n/3) + sqrt(3)*sin(2*Pi*n/3)/3 + 2n - 1);

O.g.f.: x(1+2x+16x^2)/((2x-1)^2*(4x^2+2x+1)). a(n) = 2a(n-1) + 8a(n-3) - 16a(n-4). - R. J. Mathar, Apr 28 2008

MATHEMATICA

a047240[n_] := 6 Floor[n/3] + Mod[n, 3]

a128205[n_] := Map[2^(#-1) a047240[#]&, Range[0, n]]

a128205[25] (* data *) (* Hartmut F. W. Hoft, Mar 13 2017 *)

PROG

(PARI) concat(0, Vec(x*(1 + 2*x + 16*x^2) / ((1 - 2*x)^2*(1 + 2*x + 4*x^2)) + O(x^40))) \\ Colin Barker, Mar 13 2017

CROSSREFS

Cf. A047240, A030662.

Sequence in context: A052645 A191778 A157625 * A085250 A166870 A124350

Adjacent sequences:  A128202 A128203 A128204 * A128206 A128207 A128208

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Feb 19 2007

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 16 20:45 EST 2019. Contains 320189 sequences. (Running on oeis4.)