OFFSET
0,2
COMMENTS
In general, a(n) = Sum_{k=0..floor(n/2)} C(2*k,k)*C(2*(n-2*k),n-2*k)*r^k has g.f. 1/sqrt(1-4*x-4*r*x^2+16r*x^3).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..300
FORMULA
a(n) = Sum_{k=0..floor(n/2)} C(2*k,k)*C(2*(n-2*k), n-2*k)*3^k.
D-finite with recurrence: n*a(n) +2*(1-2n)*a(n-1)+12*(1-n)*a(n-2)+24*(2n-3)*a(n-3)= 0. - R. J. Mathar, Dec 08 2011
a(n) ~ 2^(2*n+1)/sqrt(Pi*n). - Vaclav Kotesovec, Oct 17 2012
MATHEMATICA
CoefficientList[Series[1/Sqrt[1-4x-12x^2+48x^3], {x, 0, 40}], x] (* Harvey P. Dale, Jun 21 2011 *)
PROG
(PARI) x='x+O('x^50); Vec(1/sqrt(1-4*x-12*x^2+48*x^3)) \\ G. C. Greubel, Mar 16 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Apr 24 2005
STATUS
approved