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 A353820 #6 May 10 2022 14:26:37
%S A353820 1,0,-2,8,-16,96,-832,9344,-27648,238080,-4228608,55812096,-398991360,
%T A353820 4930609152,-98606039040,2440552022016,-17762113880064,
%U A353820 235149341884416,-7331825098948608,170578782435409920,-2009778629489197056,38563016760590598144,-1278044473427380666368
%N A353820 Product_{n>=1} (1 + a(n)*x^n/n!) = 1 + arctan(x).
%t A353820 nn = 23; f[x_] := Product[(1 + a[n] x^n/n!), {n, 1, nn}]; sol = SolveAlways[0 == Series[f[x] - 1 - ArcTan[x], {x, 0, nn}], x]; Table[a[n], {n, 1, nn}] /. sol // Flatten
%Y A353820 Cf. A006973, A010050, A137852, A353611, A353818, A353819, A353821.
%K A353820 sign
%O A353820 1,3
%A A353820 _Ilya Gutkovskiy_, May 08 2022