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 A097111 #12 Sep 08 2019 01:43:25
%S A097111 1,3,7,15,43,75,247,375,1363,1875,7327,9375,38683,46875,201607,234375,
%T A097111 1040803,1171875,5335087,5859375,27199723,29296875,138095767,
%U A097111 146484375,698867443,732421875,3527891647,3662109375,17773675963,18310546875
%N A097111 Expansion of (1 + 3x - 2x^2 - 12x^3)/(1 - 9x^2 + 20x^4).
%H A097111 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,9,0,-20).
%F A097111 G.f.: 3*(1+x)/(1-5x^2) - 2/(1-4x^2);
%F A097111 a(n) = 9*a(n-2) - 20*a(n-4);
%F A097111 a(n) = (3/2 + 3*sqrt(5)/10)*(sqrt(5))^n + (3/2 - 3*sqrt(5)/10)*(-sqrt(5))^n - 2^(n+1)*(1+(-1)^n)/2;
%F A097111 a(n) = Sum_{k=0..n} binomial(floor(n/2), floor(k/2))*2^k.
%Y A097111 Cf. A005053 (bisection), A193656 (bisection?).
%K A097111 easy,nonn
%O A097111 0,2
%A A097111 _Paul Barry_, Jul 25 2004