OFFSET
0,3
COMMENTS
a(n) <= A003024(n).
LINKS
Marco Kuhlmann, Tabulation of Noncrossing Acyclic Digraphs, arXiv preprint arXiv:1504.04993 [cs.DS], 2015.
M. Kuhlmann, P. Jonsson, Parsing to Noncrossing Dependency Graphs, Transactions of the Association for Computational Linguistics, vol. 3, pp. 559-570, 2015.
MathOverflow, What is the number of noncrossing acyclic digraphs?
Anssi Yli-Jyrä and Carlos Gómez-Rodríguez, Generic Axiomatization of Families of Noncrossing Graphs in Dependency Parsing, arXiv:1706.03357 [cs.CL], 2017.
FORMULA
G.f.: x*g(x) where (x+1)*g(x)^3+(x^2-2)*g(x)^2+2*x*g(x)+1 = 0. - Robert Israel, Sep 02 2014
MAPLE
S:= series(RootOf((x+1)*y^3+(x^2-2)*y^2+2*x*y+1, y, 1), x, 30):
seq(coeff(S, x, n-1), n=1..30); # Robert Israel, Sep 02 2014
MATHEMATICA
S = Root[(x+1)y^3 + (x^2-2)y^2 + 2x y + 1, y, 2] + O[x]^30;
Prepend[CoefficientList[S, x], 1] (* Jean-François Alcover, Sep 18 2018, after Robert Israel *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jordan Tirrell, Sep 02 2014
EXTENSIONS
a(11) to a(21) computed by Robert Israel, Sep 02 2014
STATUS
approved