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 A362857 #18 Aug 05 2025 05:13:57
%S A362857 1,-1,4,7,120,1373,21028,373931,7670736,178064281,4615519884,
%T A362857 132139421423,4141235867992,141016013784917,5184372688776180,
%U A362857 204668397165154867,8635388122600110240,387787185320578895537,18467131524896950511644
%N A362857 Expansion of e.g.f. exp(-2*x) / (1 + LambertW(-x)).
%H A362857 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LambertW-Function.html">Lambert W-Function</a>.
%F A362857 G.f.: Sum_{k>=0} (k*x)^k / (1 + 2*x)^(k+1).
%F A362857 a(n) = Sum_{k=0..n} (-2)^(n-k) * k^k * binomial(n,k).
%F A362857 a(n) ~ exp(-2*exp(-1)) * n^n. - _Vaclav Kotesovec_, Aug 05 2025
%t A362857 With[{nn=20},CoefficientList[Series[Exp[-2x]/(1+LambertW[-x]),{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Aug 26 2023 *)
%o A362857 (PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(exp(-2*x)/(1 + lambertw(-x))))
%Y A362857 Column k=2 of A362856.
%Y A362857 Cf. A362859.
%K A362857 sign
%O A362857 0,3
%A A362857 _Seiichi Manyama_, May 05 2023