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 A303391 #11 Feb 14 2019 02:06:04
%S A303391 1,8,40,200,872,3720,15400,62920,254440,1024648,4112680,16483400,
%T A303391 66000360,264150920,1056903080,4228272200,16914393832,67660396040,
%U A303391 270647139240,1082600410440,4330424811880,17321748357640,69287088965800,277148557003720,1108594618342760
%N A303391 Expansion of Product_{k>=1} (1 + 4*x^k)/(1 - 4*x^k).
%H A303391 Robert Israel, <a href="/A303391/b303391.txt">Table of n, a(n) for n = 0..1600</a>
%F A303391 a(n) ~ c * 4^n, where c = QPochhammer[-1, 1/4] / QPochhammer[1/4] = 3.9385207073365388638943873939345313401323799...
%p A303391 N:= 50: # for a(0)..a(N)
%p A303391 G:= mul((1+4*x^k)/(1-4*x^k),k=1..N):
%p A303391 S:= series(G,x,N+1):
%p A303391 seq(coeff(S,x,j),j=0..N); # _Robert Israel_, Feb 13 2019
%t A303391 nmax = 25; CoefficientList[Series[Product[(1+4*x^k)/(1-4*x^k), {k, 1, nmax}], {x, 0, nmax}], x]
%Y A303391 Cf. A261568, A246936, A067855, A303350.
%Y A303391 Cf. A015128, A261584, A303390.
%K A303391 nonn
%O A303391 0,2
%A A303391 _Vaclav Kotesovec_, Apr 23 2018