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 A321968 #6 Jul 21 2019 04:22:49
%S A321968 -1,3,7,55,735,13851,336743,10024911,353109375,14361853555,
%T A321968 662358958599,34154042002983,1947046027041503,121593475341796875,
%U A321968 8255204941334951655,605377094064557529151,47687467918910168180223,4015909348423983176411619
%N A321968 a(n) = 2^n*n!*[x^n] -sqrt(exp(LambertW(-x)))*(LambertW(-x) + 1).
%p A321968 -sqrt(exp(LambertW(-x)))*(LambertW(-x) + 1): series(%, x, 32):
%p A321968 seq(2^n*n!*coeff(%, x, n), n=0..17);
%t A321968 a[n_] := 2^n n! SeriesCoefficient[-Sqrt[Exp[ProductLog[-x]]] (ProductLog[ -x ] + 1), {x, 0, n}]; Table[a[n], {n, 0, 17}] (* _Jean-François Alcover_, Jul 21 2019 *)
%Y A321968 Cf. A085527.
%K A321968 sign
%O A321968 0,2
%A A321968 _Peter Luschny_, Dec 07 2018