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 A304082 #6 May 06 2018 06:29:47
%S A304082 0,1,1,3,3,11,9,35,33,105,105,339,313,1035,1017,3115,3099,9579,9345,
%T A304082 28947,28713,86979,86825,263187,260865,791577,789497,2376555,2374521,
%U A304082 7150443,7129401,21471315,21450489,64431843,64413177,193487947,193292811,580650075
%N A304082 a(n) = 3^n - A006952(n).
%F A304082 a(n) ~ 3^(n/2) / 2 if n is even and a(n) ~ 3^((n+1)/2) / 2 if n is odd.
%F A304082 a(n) ~ (1+sqrt(3) + (-1)^n*(1-sqrt(3))) * 3^(n/2) / 4.
%t A304082 nmax = 60; 3^Range[0, nmax] - CoefficientList[Series[Product[(1 - x^k)/(1 - 3*x^k), {k, 1, nmax}], {x, 0, nmax}], x]
%Y A304082 Cf. A006952, A264687.
%K A304082 nonn
%O A304082 0,4
%A A304082 _Vaclav Kotesovec_, May 06 2018