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 A336958 #5 Aug 10 2020 00:20:18
%S A336958 1,-1,-2,10,24,-312,-560,19472,6272,-1994624,4072704,299059968,
%T A336958 -1635814400,-60723321856,628215191552,15716076562432,
%U A336958 -274420622327808,-4900668238036992,140182198527655936,1717697481518809088,-83651335147070685184,-590374211868638314496
%N A336958 E.g.f.: 1 / (exp(2*x) - x).
%F A336958 a(n) = n! * Sum_{k=0..n} (-2 * (n-k+1))^k / k!.
%F A336958 a(0) = 1; a(n) = -n * a(n-1) - Sum_{k=2..n} binomial(n,k) * 2^k * a(n-k).
%t A336958 nmax = 21; CoefficientList[Series[1/(Exp[2 x] - x), {x, 0, nmax}], x] Range[0, nmax]!
%t A336958 Table[n! Sum[(-2 (n - k + 1))^k/k!, {k, 0, n}], {n, 0, 21}]
%t A336958 a[0] = 1; a[n_] := a[n] = -n a[n - 1] - Sum[Binomial[n, k] 2^k a[n - k], {k, 2, n}]; Table[a[n], {n, 0, 21}]
%Y A336958 Cf. A089148, A336947, A336959.
%K A336958 sign
%O A336958 0,3
%A A336958 _Ilya Gutkovskiy_, Aug 09 2020