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 A005330 M3992 #23 Dec 28 2024 02:01:19
%S A005330 1,5,40,644,21496,1471460,204062440,56865072164,31688930152696,
%T A005330 35223651007587140,78001790003385408040,343983307379873262633284,
%U A005330 3020895063527811952260491896,52843677532033943174017588842020,1841795434229559227318546660111716840
%N A005330 Certain subgraphs of a directed graph.
%D A005330 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A005330 E. Andresen, K. Kjeldsen, <a href="http://dx.doi.org/10.1016/0012-365X(76)90054-6">On certain subgraphs of a complete transitively directed graph</a>, Discrete Math. 14 (1976), no. 2, 103-119.
%F A005330 a(n) = Sum_{i=0..n-2} (C(n-1, i) * p(n-1-i) * Sum_{j=0..n-2-i} (-1)^j * (n-1-i-j) / p(j)) where p(n) = Product_{k=1..n} (2^k-1). - _Sean A. Irvine_, May 10 2016
%o A005330 (PARI) p(n) = prod(k=1, n, 2^k-1);
%o A005330 a(n) = sum(i=0, n-2, binomial(n-1, i) * p(n-1-i) * sum(j=0, n-2-i, (-1)^j * (n-1-i-j) / p(j))); \\ _Michel Marcus_, May 10 2016
%K A005330 nonn
%O A005330 2,2
%A A005330 _N. J. A. Sloane_
%E A005330 More terms from _Sean A. Irvine_, May 10 2016