login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A180222 a(n) = 4*a(n-1) + 8*a(n-2), with a(1)=0 and a(2)=1. 14
0, 1, 4, 24, 128, 704, 3840, 20992, 114688, 626688, 3424256, 18710528, 102236160, 558628864, 3052404736, 16678649856, 91133837312, 497964548096, 2720928890880, 14867431948288, 81237158920192, 443888091267072, 2425449636429824, 13252903275855872 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Nathaniel Johnston, Table of n, a(n) for n = 1..500

Index entries for linear recurrences with constant coefficients, signature (4,8).

FORMULA

a(n) = 2^(n-3)*((1+sqrt(3))^(n-1)-(1-sqrt(3))^(n-1))/sqrt(3). - Rolf Pleisch, May 14 2011

a(n) = (-1)^n*A174443(n-1). - Nathaniel Johnston, May 14 2011

G.f.: x^2/(1-4*x-8*x^2).

a(n+2) = Sum_{k=0..n} A201947(n,k)*3^(n-k). - Philippe Deléham, Dec 07 2011

a(n+2) = 2^n*A002605(n+1). - R. J. Mathar, May 07 2019

MATHEMATICA

Join[{a=0, b=1}, Table[c=4*b+8*a; a=b; b=c, {n, 100}]]

LinearRecurrence[{4, 8}, {0, 1}, 30] (* G. C. Greubel, Jan 16 2018 *)

PROG

(PARI) concat(0, Vec(1/(1-4*x-8*x^2)+O(x^98))) \\ Charles R Greathouse IV, Dec 07 2011

(MAGMA) I:=[0, 1]; [n le 2 select I[n] else 4*Self(n-1) + 8*Self(n-2): n in [1..30]]; // G. C. Greubel, Jan 16 2018

CROSSREFS

Sequence in context: A103455 A289715 A174443 * A192070 A048180 A057391

Adjacent sequences:  A180219 A180220 A180221 * A180223 A180224 A180225

KEYWORD

nonn,easy

AUTHOR

Vladimir Joseph Stephan Orlovsky, Jan 16 2011

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 November 30 14:29 EST 2020. Contains 338802 sequences. (Running on oeis4.)