OFFSET
0,3
COMMENTS
What does this sequence count?
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
FORMULA
From Vaclav Kotesovec, Mar 01 2014: (Start)
G.f.: 2*(1-x)/(1 - 2*x + x^3 + sqrt(1 - 4*x + 4*x^2 - 2*x^3 + x^6)).
D-finite with Recurrence: (n+3)*a(n) = 2*(2*n+3)*a(n-1) - 4*n*a(n-2) + (2*n-3)*a(n-3) - (n-6)*a(n-6).
a(n) ~ (6*r^2+14*r+17) * sqrt(7*r-2) / (2 * sqrt(Pi) * n^(3/2) * r^(n-1/2)), where r = 1/3*(-2 - 2*(2/(47 + 3*sqrt(249)))^(1/3) + (1/2*(47 + 3*sqrt(249)))^(1/3)) = 0.3532099641993244294831... is the root of the equation r^3 + 2*r^2 + 2*r = 1.
(End)
G.f. A(q) satisfies 0 = -q^3*A(q)^2 + (q^3 - 2*q + 1)*A(q) + (q - 1).
MATHEMATICA
CoefficientList[Series[2*(1-x)/(1 - 2*x + x^3 + Sqrt[1 - 4*x + 4*x^2 - 2*x^3 + x^6]), {x, 0, 20}], x] (* Vaclav Kotesovec, Mar 01 2014 *)
PROG
(PARI) N = 66; q = 'q + O('q^N);
G(k) = if(k>N, 1, 1 - q/(1 - q - q^3 / G(k+1) ) );
Vec( 1/G(0) )
CROSSREFS
KEYWORD
nonn
AUTHOR
Joerg Arndt, Feb 27 2014
STATUS
approved