OFFSET
0,2
COMMENTS
Counts colored Motzkin paths, where H(1,0) and U(1,1) each have 6 colors and D(1,-1) one color. - Paul Barry, May 16 2005
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
FORMULA
G.f.: (1-6*x-sqrt(1-12*x+12*x^2))/(12*x^2).
a(n) = Sum_{k=0..n} 1/(k+1) * C(k+1,n-k+1) * C(n,k) * 6^k.
E.g.f.: a(n) = n! * [x^n] exp(6*x)*BesselI(1, 2*sqrt(6)*x)/(sqrt(6)*x). -Peter Luschny, Aug 25 2012
D-finite with recurrence: (n+2)*a(n) = 6*(2*n+1)*a(n-1) - 12*(n-1)*a(n-2). - Vaclav Kotesovec, Oct 17 2012
a(n) ~ sqrt(44+18*sqrt(6))*(6+2*sqrt(6))^n/(2*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Oct 17 2012
G.f.: 1/(1 - 6*x - 6*x^2/(1 - 6*x - 6*x^2/(1 - 6*x - 6*x^2/(1 - 6*x - 6*x^2/(1 - ...))))), a continued fraction. - Ilya Gutkovskiy, Sep 21 2017
MATHEMATICA
CoefficientList[Series[(1-6*x-Sqrt[1-12*x+12*x^2])/(12*x^2), {x, 0, 20}], x] (* Vaclav Kotesovec, Oct 17 2012 *)
PROG
(PARI) x='x+O('x^66); Vec((1-6*x-sqrt(1-12*x+12*x^2))/(12*x^2)) \\ Joerg Arndt, May 15 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, May 15 2005
STATUS
approved