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 A348860 #7 Nov 02 2021 09:51:11
%S A348860 1,0,1,4,37,632,20905,1359692,175426573,45086173824,23129393794129,
%T A348860 23707675064224020,48577049664823958389,199020196349510773741576,
%U A348860 1630572517436087330046884473,26716930897552073378560239594588,875487110213852689248519499248558685
%N A348860 G.f. A(x) satisfies: A(x) = 1 / ((1 + x) * (1 - x * A(2*x))).
%F A348860 a(n) = (-1)^n + Sum_{k=0..n-1} 2^k * a(k) * a(n-k-1).
%F A348860 a(n) ~ c * 2^(n*(n-1)/2), where c = 0.658663398267275680037834076118178644268023291808559507713140088111498143... - _Vaclav Kotesovec_, Nov 02 2021
%t A348860 nmax = 16; A[_] = 0; Do[A[x_] = 1/((1 + x) (1 - x A[2 x])) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
%t A348860 a[n_] := a[n] = (-1)^n + Sum[2^k a[k] a[n - k - 1], {k, 0, n - 1}]; Table[a[n], {n, 0, 16}]
%Y A348860 Cf. A005043, A015083, A348861, A348862.
%K A348860 nonn
%O A348860 0,4
%A A348860 _Ilya Gutkovskiy_, Nov 02 2021