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 A001446 #18 Feb 01 2022 23:58:35 %S A001446 10,34,136,520,2080,8224,32896,131200,524800,2097664,8390656,33556480, %T A001446 134225920,536879104,2147516416,8589967360,34359869440,137439084544, %U A001446 549756338176,2199023779840,8796095119360 %N A001446 a(n) = (4^n + 4^[ n/2 ] )/2. %H A001446 James Spahlinger, <a href="/A001446/b001446.txt">Table of n, a(n) for n = 2..1001</a> %H A001446 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,4,-16). %F A001446 G.f.: x^2*(10-6x-40x^2)/((1-4x)*(1-4x^2)). %F A001446 a(n) = 4*a(n-1) + 4*a(n-2) - 16*a(n-3) for n > 4. - _Chai Wah Wu_, Sep 10 2020 %Y A001446 Equals 2^(2[n/2]-1) * (A056450(n)+1). Cf. A001445. %K A001446 nonn,easy %O A001446 2,1 %A A001446 _N. J. A. Sloane_