OFFSET
0,3
FORMULA
a(n) = T(2*n,n), where T(n,k) = A...(n,k).
a(n) = sum(binomial(2*n-2*i-1,n-2*i)*3^i,i=0..n/2).
G.f.: (2-11*x+12*x^2+(2-9*x)*sqrt(1-4*x))/(2*(1-4*x)*(2-6*x-9*x^2)).
Conjecture: 2*n*(n+3)*a(n) +2*(-7*n^2-19*n+24)*a(n-1) +3*(5*n^2+11*n-48)*a(n-2) +18*(n+4)*(2*n-3)*a(n-3)=0. - R. J. Mathar, Jun 14 2016
Conjecture: +4*n*a(n) +2*(-23*n+22)*a(n-1) +156*(n-2)*a(n-2) +9*(-7*n+38)*a(n-3) +162*(-2*n+5)*a(n-4)=0. - R. J. Mathar, Jun 14 2016
MATHEMATICA
Table[Sum[Binomial[2n-2i-1, n-2i]3^i, {i, 0, n/2}], {n, 0, 25}]
CoefficientList[Series[(2-11x+12x^2+(2-9x)Sqrt[1-4x])/(2(1-4x)(2- 6x-9x^2)), {x, 0, 30}], x] (* Harvey P. Dale, Jun 10 2011 *)
PROG
(Maxima) makelist(sum(binomial(2*n-2*i-1, n-2*i)*3^i, i, 0, n/2), n, 0, 25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emanuele Munarini, Jun 07 2011
STATUS
approved