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 A305209 #5 May 27 2018 19:47:14
%S A305209 1,1,2,12,86,885,11234,172711,3112262,64422126,1506406702,39279802969,
%T A305209 1130133725736,35566642690293,1215444767739120,44823725114186355,
%U A305209 1774344335649148230,75042087586212893216,3377041177800135323864,161125608740713509132809,8124438293071792011560256
%N A305209 a(n) = [x^n] exp(Sum_{k>=1} (-1)^(k+1)*x^k/(k*(1 - n*x^k))).
%H A305209 N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>
%F A305209 a(n) = [x^n] Product_{k>=1} (1 + x^k)^(n^(k-1)).
%t A305209 Table[SeriesCoefficient[Exp[Sum[(-1)^(k + 1) x^k/(k (1 - n x^k)), {k, 1, n}]], {x, 0, n}], {n, 0, 20}]
%t A305209 Table[SeriesCoefficient[Product[(1 + x^k)^(n^(k - 1)), {k, 1, n}], {x, 0, n}], {n, 0, 20}]
%Y A305209 Cf. A098407, A292805, A305207.
%K A305209 nonn
%O A305209 0,3
%A A305209 _Ilya Gutkovskiy_, May 27 2018