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 A039647 #23 Oct 16 2023 01:36:25
%S A039647 1,3,8,42,264,2160,20880,236880,3064320,44634240,722131200,
%T A039647 12853209600,249559833600,5249378534400,118911189196800,
%U A039647 2886037330176000,74715282690048000,2055161959538688000,59855791774851072000,1840125433884401664000,59547709552131440640000
%N A039647 Related to A000032 (Lucas numbers): (n-1)!*L(n).
%C A039647 Number of possible well-colored circuits.
%H A039647 C. Banderier, J.-M. Le Bars, and V. Ravelomanana, <a href="https://arxiv.org/abs/math/0411138">Generating functions for kernels of digraphs</a>, arXiv:math/0411138 [math.CO], 2004.
%F A039647 a(n) = (n-1)!*L(n), L(n) := A000032(n); E.g.f.: -log(1-x-x^2). Also a(n)/n! = sum(binomial(n-j, j)/(n-j), j=0..floor(n/2)).
%F A039647 a(n) = (n-1)*(a(n-1)+(n-2)*a(n-2)), for n > 2. - _Christian Krause_, Oct 15 2023
%t A039647 nn=19;Drop[Range[0,nn]!CoefficientList[Series[Log[1/(1-x-x^2)],{x,0,nn}],x],1] (* _Geoffrey Critzer_, Jul 01 2013 *)
%Y A039647 a(n) = A039692(n, 1) (first column of Fibonacci Jabotinsky-triangle).
%Y A039647 Cf. A000032, A000142.
%K A039647 easy,nonn
%O A039647 1,2
%A A039647 _Wolfdieter Lang_