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 A277507 #7 Nov 10 2017 07:38:06
%S A277507 -1,0,0,3,28,305,3846,57337,998600,20036529,456403690,11647754921,
%T A277507 329290975212,10214585950153,344897398385918,12590837785019145,
%U A277507 494101941398352016,20740772742716097377,927276395603713539282,43987299891665164562377,2206610456287703987567540
%N A277507 E.g.f.: -1/((1-LambertW(-x))*(1-x)).
%H A277507 G. C. Greubel, <a href="/A277507/b277507.txt">Table of n, a(n) for n = 0..385</a>
%F A277507 a(n) ~ n^(n-1) / (4*(1-exp(-1))).
%t A277507 CoefficientList[Series[-1/(1-LambertW[-x])/(1-x), {x, 0, 20}], x] * Range[0, 20]!
%o A277507 (PARI) x='x+O('x^50); Vec(serlaplace(-1/((1 - lambertw(-x))*(1-x)))) \\ _G. C. Greubel_, Nov 08 2017
%Y A277507 Cf. A277506, A277508.
%K A277507 sign
%O A277507 0,4
%A A277507 _Vaclav Kotesovec_, Oct 18 2016