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 A293860 #6 Oct 18 2017 04:27:08
%S A293860 0,1,4,63,1648,65075,3629196,272106555,26418426560,3225539263995,
%T A293860 483800514119500,87459323696213843,18755503692216214320,
%U A293860 4707783117485450859987,1367396879443428912151724,455052324991418691450493275,172012620929344322616321833728
%N A293860 a(0) = 0, a(1) = 1; a(n) = n! * [x^n] exp(n*x)*Sum_{k=1..n-1} a(k)*x^k/k!.
%F A293860 a(n) ~ c * n^(2*n + 1 + log(2)/2) / (log(2)^n * exp(2*n)), where c = 2.715081809041541547553157767788588016035268429424586978200936... - _Vaclav Kotesovec_, Oct 18 2017
%e A293860 E.g.f. A(x) = x + 4*x^2/2! + 63*x^3/3! + 1648*x^4/4! + 65075*x^5/5! + 3629196*x^6/6! + ...
%t A293860 a[n_] := a[n] = n! SeriesCoefficient[Exp[n x] Sum[a[k] x^k/k!, {k, 1, n - 1}], {x, 0, n}]; a[0] = 0; a[1] = 1; Table[a[n], {n, 0, 16}]
%Y A293860 Cf. A000629, A000670, A052882.
%K A293860 nonn
%O A293860 0,3
%A A293860 _Ilya Gutkovskiy_, Oct 17 2017