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 A097335 #10 May 09 2024 09:07:56
%S A097335 1,4,4,13,49,85,202,643,1408,3226,9013,21685,50719,131836,327001,
%T A097335 783472,1969996,4913005,11964253,29694217,73911262,181589539,
%U A097335 448837492,1114038850,2748344701,6787882129,16814231779,41549334088,102640273249
%N A097335 a(n) = Sum_{k=0..n} C(n-k, floor(k/2))*3^k.
%H A097335 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,9)
%F A097335 G.f. : (1+3x)/(1-x-9x^3); a(n)=a(n-1)+9a(n-3).
%Y A097335 Cf. A097333, A097334, A097336.
%K A097335 easy,nonn
%O A097335 0,2
%A A097335 _Paul Barry_, Aug 05 2004