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 A377646 #41 Nov 04 2024 09:15:22
%S A377646 1,0,4,6,32,130,432,1274,3488,9090,22880,56122,134928,319202,745136,
%T A377646 1719930,3931712,8912386,20053440,44825978,99614000,220200162,
%U A377646 484441232,1061157946,2315254752,5033163650,10905189152,23555209914,50734299728,108984793570
%N A377646 Expansion of e.g.f. (1 + x * (exp(x) - 1))^2.
%F A377646 a(n) = n! * Sum_{k=0..floor(n/2)} k! * binomial(2,k) * Stirling2(n-k,k)/(n-k)!.
%o A377646 (PARI) a(n) = n!*sum(k=0, n\2, k!*binomial(2, k)*stirling(n-k, k, 2)/(n-k)!);
%Y A377646 Cf. A377680, A377681.
%Y A377646 Cf. A375660.
%K A377646 nonn,easy
%O A377646 0,3
%A A377646 _Seiichi Manyama_, Nov 04 2024