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 A138477 #22 Sep 14 2024 06:54:00
%S A138477 0,0,1,2,3,6,15,30,55,110,231,462,903,1806,3655,7310,14535,29070,
%T A138477 58311,116622,232903,465806,932295,1864590,3727815,7455630,14913991,
%U A138477 29827982,59650503,119301006,238612935,477225870,954429895,1908859790,3817763271,7635526542
%N A138477 A084175 interleaved with 2*A084175.
%H A138477 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,2,2,-4).
%F A138477 From _R. J. Mathar_, May 19 2008: (Start)
%F A138477 O.g.f.: x^2/((2*x-1)(x-1)(1+x)(1+2*x^2)).
%F A138477 a(2n) = A084175(n). a(2n+1) = 2*A084175(n).
%F A138477 a(n) = 2*a(n-1) - a(n-2) + 2*a(n-3) + 2*a(n-4) - 4*a(n-5). (End)
%t A138477 LinearRecurrence[{2, -1, 2, 2, -4}, {0, 0, 1, 2, 3}, 40] (* _Amiram Eldar_, Sep 13 2024 *)
%Y A138477 Cf. A084175.
%K A138477 nonn,easy
%O A138477 0,4
%A A138477 _Paul Curtz_, May 18 2008
%E A138477 More terms from _R. J. Mathar_, May 19 2008