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 A377680 #8 Nov 04 2024 09:15:18
%S A377680 1,0,6,9,84,375,1998,11361,60840,299403,1368930,5906373,24362748,
%T A377680 97019247,375712470,1422455625,5286155088,19340722707,69831127242,
%U A377680 249265052301,880927979940,3086000399223,10726216043070,37020328044945,126961071656184,432900077950875
%N A377680 Expansion of e.g.f. (1 + x * (exp(x) - 1))^3.
%F A377680 a(n) = n! * Sum_{k=0..floor(n/2)} k! * binomial(3,k) * Stirling2(n-k,k)/(n-k)!.
%o A377680 (PARI) a(n) = n!*sum(k=0, n\2, k!*binomial(3, k)*stirling(n-k, k, 2)/(n-k)!);
%Y A377680 Cf. A377646, A377681.
%Y A377680 Cf. A375661.
%K A377680 nonn,easy
%O A377680 0,3
%A A377680 _Seiichi Manyama_, Nov 04 2024