OFFSET
0,2
COMMENTS
A transform of 2^n under the mapping g(x)->(1/sqrt(1-4x))g(xc(x)^2), where c(x) is the g.f. of the Catalan numbers A000108. A transform of 3^n under the mapping g(x)->(1/(c(x)*sqrt(1-4x))g(x*c(x)).
Hankel transform is A088138(n+1). - Paul Barry, Jan 11 2007
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
FORMULA
G.f.: (sqrt(1-4*x)+1)/(sqrt(1-4*x)*(3*sqrt(1-4*x)-1)).
G.f.: sqrt(1-4*x)*(sqrt(1-4*x)-3*x+1)/((1-4*x)*(2-9*x)).
a(n) = sum{k=0..n, binomial(2n, n-k)2^k}.
a(n) = sum{k=0..n, C(2n,k)*2^(n-k)}; - Paul Barry, Jan 11 2007
a(n) = sum{k=0..n, C(n+k-1,k)3^(n-k)}; - Paul Barry, Sep 28 2007
Conjecture: 2*n*a(n) +(-23*n+16)*a(n-1) +3*(29*n-44)*a(n-2) +54*(-2*n+5)*a(n-3)=0. - R. J. Mathar, Nov 24 2012
a(n) ~ (9/2)^n. - Vaclav Kotesovec, Feb 12 2014
a(n) = [x^n] 1/((1 - x)^n*(1 - 3*x)). - Ilya Gutkovskiy, Oct 12 2017
MATHEMATICA
CoefficientList[Series[Sqrt[1-4*x]*(Sqrt[1-4*x]-3*x+1)/((1-4*x)*(2-9*x)), {x, 0, 20}], x] (* Vaclav Kotesovec, Feb 12 2014 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Nov 08 2004
STATUS
approved