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 A303390 #5 Apr 23 2018 03:38:45
%S A303390 1,6,24,96,330,1104,3552,11184,34584,105990,322224,975264,2942016,
%T A303390 8857680,26631312,80005632,240219114,721036320,2163789816,6492625152,
%U A303390 19480105392,58444390176,175340344416,526034008752,1578124753152,4734415061142,14203316252400
%N A303390 Expansion of Product_{k>=1} (1 + 3*x^k)/(1 - 3*x^k).
%F A303390 a(n) ~ c * 3^n, where c = QPochhammer[-1, 1/3] / QPochhammer[1/3] = 5.5877920355220979147599292926505407983327527...
%t A303390 nmax = 30; CoefficientList[Series[Product[(1+3*x^k)/(1-3*x^k), {k, 1, nmax}], {x, 0, nmax}], x]
%Y A303390 Cf. A032308, A242587.
%Y A303390 Cf. A015128, A261584, A303391.
%K A303390 nonn
%O A303390 0,2
%A A303390 _Vaclav Kotesovec_, Apr 23 2018