This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A070876 #33 Mar 28 2022 07:42:01
%S A070876 9,15,18,30,36,60,72,120,144,240,288,480,576,960,1152,1920,2304,3840,
%T A070876 4608,7680,9216,15360,18432,30720,36864,61440,73728,122880,147456,
%U A070876 245760,294912,491520,589824,983040,1179648,1966080,2359296,3932160
%N A070876 Binary expansion is 1xx100...0 where xx = 00 or 11.
%H A070876 Vincenzo Librandi, <a href="/A070876/b070876.txt">Table of n, a(n) for n = 0..1000</a>
%H A070876 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,2).
%F A070876 From _Bruno Berselli_, Mar 02 2011: (Start)
%F A070876 G.f.: 3*(3+5*x)/(1-2*x^2).
%F A070876 a(n) = 3*(4-(-1)^n)*2^((2*n+(-1)^n-1)/4). Therefore: a(n) = 9*2^(n/2) for n even, otherwise a(n) = 15*2^((n-1)/2).
%F A070876 a(n) = 2*a(n-2) for n>1. (End)
%F A070876 Sum_{n>=0} 1/a(n) = 16/45. - _Amiram Eldar_, Mar 28 2022
%t A070876 a = {}; Do[a = Append[a, FromDigits[ Join[{1, 0, 0, 1}, Table[0, {n}]], 2]]; a = Append[a, FromDigits[ Join[{1, 1, 1, 1}, Table[0, {n}]], 2]], {n, 0, 20}]; a
%t A070876 CoefficientList[Series[3 (3 + 5 x) / (1 - 2 x^2), {x, 0, 40}], x] (* _Vincenzo Librandi_, Jun 19 2013 *)
%t A070876 LinearRecurrence[{0,2},{9,15},40] (* _Harvey P. Dale_, Aug 06 2021 *)
%o A070876 (Magma) [n le 2 select 6*n+3 else 2*Self(n-2): n in [1..38]]; // _Bruno Berselli_, Mar 02 2011
%o A070876 (PARI) my(x='x+O('x^99)); Vec(3*(3+5*x)/(1-2*x^2)) \\ _Altug Alkan_, Sep 20 2018
%Y A070876 Cf. A070875.
%K A070876 nonn,base,easy
%O A070876 0,1
%A A070876 _N. J. A. Sloane_, May 19 2002
%E A070876 More terms from _Robert G. Wilson v_, May 20 2002