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 A383986 #10 May 21 2025 01:26:30
%S A383986 0,1,-1,1,-13,61,-601,5881,-73333,1021861,-16334401,290146561,
%T A383986 -5707536253,122821558861,-2873553719401,72586328036041,
%U A383986 -1969306486088773,57106504958139061,-1762735601974347601,57705363524117482321,-1996916624448159410893
%N A383986 Expansion of the exponential generating function sqrt(4*exp(x) - exp(2*x) - 2) - 1.
%H A383986 Michael De Vlieger, <a href="/A383986/b383986.txt">Table of n, a(n) for n = 0..409</a>
%H A383986 Bérénice Delcroix-Oger and Clément Dupont, <a href="https://arxiv.org/abs/2505.06094">Lie-operads and operadic modules from poset cohomology</a>, arXiv:2505.06094 [math.CO], 2025. See p. 28, Table 2, operad "NAC_2".
%t A383986 nn = 20; f[x_] := -1 + Sqrt[1 + 2 x - x^2];
%t A383986 Range[0, nn]! * CoefficientList[Series[f[-(1 - Exp[x])], {x, 0, nn}], x]
%Y A383986 Cf. A002050, A006531, A084099, A101851, A114285, A182037, A225883, A383985, A383987, A383988, A383989.
%K A383986 sign,easy
%O A383986 0,5
%A A383986 _Michael De Vlieger_, May 16 2025