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 A362340 #12 Feb 16 2025 08:34:05
%S A362340 1,1,0,-2,7,51,-239,-2435,16353,209377,-1826099,-28232379,303020125,
%T A362340 5494172893,-70032035163,-1457369472299,21512472563281,
%U A362340 505400696581905,-8478758871011807,-221971772323923263,4171251104170567101,120416449897739144941
%N A362340 a(n) = n! * Sum_{k=0..floor(n/2)} (-k/2)^k / (k! * (n-2*k)!).
%H A362340 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LambertW-Function.html">Lambert W-Function</a>.
%F A362340 E.g.f.: exp(x) / (1 + LambertW(x^2/2)).
%o A362340 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(exp(x)/(1+lambertw(x^2/2))))
%Y A362340 Cf. A069856, A362341, A362342.
%Y A362340 Cf. A362276.
%K A362340 sign
%O A362340 0,4
%A A362340 _Seiichi Manyama_, Apr 17 2023