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 A331617 #11 Jan 26 2020 11:26:56
%S A331617 1,1,3,11,49,265,1683,12035,95169,832337,7998467,83033403,922112305,
%T A331617 10978263257,139956480467,1889161216179,26798589518593,
%U A331617 401123509624737,6346168059440515,105040097140558699,1805102151607613361,32421358229074354601
%N A331617 E.g.f.: exp(1 / (1 - arctan(x)) - 1).
%C A331617 a(53) is negative. - _Vaclav Kotesovec_, Jan 26 2020
%H A331617 Vaclav Kotesovec, <a href="/A331617/b331617.txt">Table of n, a(n) for n = 0..400</a>
%F A331617 a(0) = 1; a(n) = Sum_{k=1..n} binomial(n-1,k-1) * A191700(k) * a(n-k).
%t A331617 nmax = 21; CoefficientList[Series[Exp[1/(1 - ArcTan[x]) - 1], {x, 0, nmax}], x] Range[0, nmax]!
%t A331617 A191700[0] = 1; A191700[n_] := A191700[n] = Sum[Binomial[n, k] If[OddQ[k], (-1)^Boole[IntegerQ[(k + 1)/4]] (k - 1)!, 0] A191700[n - k], {k, 1, n}]; a[0] = 1; a[n_] := a[n] = Sum[Binomial[n - 1, k - 1] A191700[k] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 21}]
%o A331617 (PARI) seq(n)={Vec(serlaplace(exp(1/(1 - atan(x + O(x*x^n))) - 1)))} \\ _Andrew Howroyd_, Jan 22 2020
%Y A331617 Cf. A002019, A110708, A191700, A331610, A331615, A331616, A331618.
%K A331617 sign
%O A331617 0,3
%A A331617 _Ilya Gutkovskiy_, Jan 22 2020