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 A303345 #21 Apr 25 2018 03:14:21
%S A303345 1,-2,0,-2,6,-6,12,-22,48,-94,160,-318,622,-1210,2268,-4482,8678,
%T A303345 -16998,32632,-64366,124674,-245866,476108,-940866,1829148,-3617066,
%U A303345 7040112,-13937530,27186810,-53857062,105196572,-208546726,407944704,-809175966,1584713040
%N A303345 Expansion of Product_{k>=1} ((1 - 2*x^k)/(1 + 2*x^k))^(1/2).
%H A303345 Seiichi Manyama, <a href="/A303345/b303345.txt">Table of n, a(n) for n = 0..3000</a>
%F A303345 a(n) ~ c * (-2)^n / sqrt(Pi*n), where c = (QPochhammer[-1, -1/2] / QPochhammer[-1/2])^(1/2) = 0.96924509195711964009315.... - _Vaclav Kotesovec_, Apr 25 2018
%p A303345 seq(coeff(series(mul(((1-2*x^k)/(1+2*x^k))^(1/2), k = 1..n), x, n+1), x, n), n=0..40); # _Muniru A Asiru_, Apr 22 2018
%o A303345 (PARI) N=66; x='x+O('x^N); Vec(prod(k=1, N, ((1-2*x^k)/(1+2*x^k))^(1/2)))
%Y A303345 Cf. A303306, A303346, A303439.
%Y A303345 Expansion of Product_{k>=1} ((1 - 2^b*x^k)/(1 + 2^b*x^k))^(1/(2^b)): A002448 (b=0), this sequence (b=1), A303387 (b=2), A303396 (b=3).
%K A303345 sign
%O A303345 0,2
%A A303345 _Seiichi Manyama_, Apr 22 2018