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 A383987 #23 May 24 2025 00:20:56
%S A383987 0,1,-5,49,-725,14401,-360005,10863889,-384415925,15612336481,
%T A383987 -715930020005,36592369889329,-2062911091119125,127170577711282561,
%U A383987 -8510569547826528005,614491222512504748369,-47615614242877583230325,3941408640018910366196641
%N A383987 Series expansion of the exponential generating function -tridend(-(1-exp(x))) where tridend(x) = (1 - 3*x - sqrt(1+6*x+x^2)) / (4*x) (A001003).
%H A383987 Michael De Vlieger, <a href="/A383987/b383987.txt">Table of n, a(n) for n = 0..353</a>
%H A383987 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, triassociative operad "Trias".
%t A383987 nn = 17; f[x_] := (1 + 3*x - Sqrt[1 + 6*x + x^2])/(4*x); Range[0, nn]! * CoefficientList[Series[f[-(1 - Exp[x])], {x, 0, nn}], x]
%Y A383987 Cf. A002050, A006531, A084099, A101851, A114285, A225883, A383985, A383986, A383988, A383989, A383991.
%Y A383987 Composition of A001003 with exp(x)-1.
%K A383987 sign,easy
%O A383987 0,3
%A A383987 _Michael De Vlieger_, May 16 2025