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 A277490 #9 Nov 10 2017 07:37:32
%S A277490 -1,0,2,12,72,520,5040,67284,1156736,23655888,549676800,14216252380,
%T A277490 405068387328,12624364306008,427599019108352,15646376279614500,
%U A277490 615155126821355520,25861820048469628576,1157706908035331457024,54977324662490442177708,2760439046217459138560000
%N A277490 E.g.f.: -1/(1+LambertW(-x)^2).
%H A277490 G. C. Greubel, <a href="/A277490/b277490.txt">Table of n, a(n) for n = 0..385</a>
%F A277490 a(n) ~ n^(n-1) / 2.
%t A277490 CoefficientList[Series[-1/(1+LambertW[-x]^2), {x, 0, 20}], x] * Range[0, 20]!
%o A277490 (PARI) x='x+O('x^50); Vec(serlaplace(-1/(1 + lambertw(-x)^2))) \\ _G. C. Greubel_, Nov 08 2017
%Y A277490 Cf. A063170, A134095.
%K A277490 sign
%O A277490 0,3
%A A277490 _Vaclav Kotesovec_, Oct 17 2016