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 A277503 #7 Nov 13 2017 02:45:54
%S A277503 0,1,2,7,48,469,5584,80235,1367040,26840841,595623680,14752565807,
%T A277503 403579762688,12084385256605,393093330282496,13804177426246995,
%U A277503 520496287836012544,20973496057176404881,899452315670554017792,40903215737685386469847
%N A277503 E.g.f.: -LambertW(-arctan(x)).
%H A277503 G. C. Greubel, <a href="/A277503/b277503.txt">Table of n, a(n) for n = 0..385</a>
%F A277503 a(n) ~ sqrt(sin(2*exp(-1))/2) * exp(-n + 1/2) * n^(n-1) / tan(exp(-1))^n.
%t A277503 CoefficientList[Series[-LambertW[-ArcTan[x]], {x, 0, 20}], x] * Range[0, 20]!
%o A277503 (PARI) x='x+O('x^50); concat([0], Vec(serlaplace(-lambertw(-atan(x))))) \\ _G. C. Greubel_, Nov 12 2017
%Y A277503 Cf. A277502.
%K A277503 nonn
%O A277503 0,3
%A A277503 _Vaclav Kotesovec_, Oct 18 2016