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 A367881 #7 Dec 04 2023 06:35:55
%S A367881 1,0,6,9,228,1095,23238,215481,4657992,66216555,1553967210,
%T A367881 29793656013,777115661292,18608934688383,542832959656302,
%U A367881 15470567460571905,503794462155308688,16557037363336856019,598704921471691072242,22205328374455141122165
%N A367881 Expansion of e.g.f. 1/(1 - 3 * x * (exp(x) - 1)).
%F A367881 a(0) = 1; a(n) = 3 * n * Sum_{k=2..n} binomial(n-1,k-1) * a(n-k).
%F A367881 a(n) = n! * Sum_{k=0..floor(n/2)} 3^k * k! * Stirling2(n-k,k)/(n-k)!.
%o A367881 (PARI) a(n) = n!*sum(k=0, n\2, 3^k*k!*stirling(n-k, k, 2)/(n-k)!);
%Y A367881 Cf. A052848, A367880.
%K A367881 nonn
%O A367881 0,3
%A A367881 _Seiichi Manyama_, Dec 03 2023