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 A277508 #7 Nov 10 2017 07:38:14
%S A277508 -1,2,-4,15,-44,385,-294,32473,280120,8528049,170757910,4748977321,
%T A277508 132530188308,4210910824393,142940443542274,5273270156096265,
%U A277508 208276214340505456,8800344095155520353,395536292522024420142,18853858817276143333321,949787282108877829653580
%N A277508 E.g.f.: -1/((1-LambertW(-x))*(1+x)).
%H A277508 G. C. Greubel, <a href="/A277508/b277508.txt">Table of n, a(n) for n = 0..385</a>
%F A277508 a(n) ~ n^(n-1) / (4*(1+exp(-1))).
%t A277508 CoefficientList[Series[-1/(1-LambertW[-x])/(1+x), {x, 0, 20}], x] * Range[0, 20]!
%o A277508 (PARI) x='x+O('x^50); Vec(serlaplace(-1/((1 - lambertw(-x))*(1+x)))) \\ _G. C. Greubel_, Nov 08 2017
%Y A277508 Cf. A277507, A277509.
%K A277508 sign
%O A277508 0,2
%A A277508 _Vaclav Kotesovec_, Oct 18 2016