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 A331334 #11 Jul 11 2020 02:33:35
%S A331334 1,0,-4,32,-240,1792,-11840,26112,1589504,-57548800,1556757504,
%T A331334 -39250780160,973563695104,-24122607992832,596246557736960,
%U A331334 -14477682566889472,332039052050104320,-6425352382711857152,53086817854485692416,4505005802471597015040,-419037805969718712991744
%N A331334 a(n) = n! * [x^n] exp(1 - 1/(2*x + 1))/(2*x + 1).
%F A331334 a(n) = 4*(1 - n)*((n - 1)*a(n - 2) + a(n - 1)).
%F A331334 a(n) = (-2)^n*Sum_{k=0..n} A331333(n, k)/(-2)^k.
%F A331334 a(n)/(-2)^n = n!*LaguerreL(n, 1) = A009940(n).
%p A331334 gf := exp(1 - 1/(2*x + 1))/(2*x + 1): ser := series(gf, x, 32):
%p A331334 seq(n!*coeff(ser, x, n), n=0..20);
%p A331334 # Alternative:
%p A331334 a := proc(n) option remember; if n < 2 then 1 - n else
%p A331334 4*(1 - n)*((n - 1)*a(n - 2) + a(n - 1)) fi end: seq(a(n), n=0..20);
%Y A331334 Cf. A331333, A009940.
%K A331334 sign
%O A331334 0,3
%A A331334 _Peter Luschny_, Jan 19 2020