OFFSET
1,2
COMMENTS
Number of possible well-colored circuits.
LINKS
C. Banderier, J.-M. Le Bars, and V. Ravelomanana, Generating functions for kernels of digraphs, arXiv:math/0411138 [math.CO], 2004.
FORMULA
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)).
a(n) = (n-1)*(a(n-1)+(n-2)*a(n-2)), for n > 2. - Christian Krause, Oct 15 2023
MATHEMATICA
nn=19; Drop[Range[0, nn]!CoefficientList[Series[Log[1/(1-x-x^2)], {x, 0, nn}], x], 1] (* Geoffrey Critzer, Jul 01 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
STATUS
approved