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 A352011 #5 Mar 01 2022 07:28:08
%S A352011 1,1,1,-3,-7,5,33,269,393,-1451,-4815,-14115,-2791,171685,398145,
%T A352011 -3887699,-10399319,6567925,63031889,558518141,853157689,-4400392635,
%U A352011 -14954126751,29904043597,151457170889,344861133205,170895616881,-12627954103779,-30049168949927
%N A352011 a(0) = 1; a(n) = Sum_{k=0..floor((n-1)/2)} (-4)^k * a(k) * a(n-2*k-1).
%F A352011 G.f. A(x) satisfies: A(x) = 1 / (1 - x * A(-4*x^2)).
%t A352011 a[0] = 1; a[n_] := a[n] = Sum[(-4)^k a[k] a[n - 2 k - 1], {k, 0, Floor[(n - 1)/2]}]; Table[a[n], {n, 0, 28}]
%t A352011 nmax = 28; A[_] = 0; Do[A[x_] = 1/(1 - x A[-4 x^2]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
%Y A352011 Cf. A015099, A101912, A352009, A352010.
%K A352011 sign
%O A352011 0,4
%A A352011 _Ilya Gutkovskiy_, Feb 28 2022