OFFSET
0,4
LINKS
FORMULA
G.f. A(x) = 1+B'(x)*(1-x/B(x))^2, where B(x)/x is g.f. of A001764.
a(n) = Sum_{k=1..n}(k*binomial(n-1,k-2)*binomial(2*n,n-k))/n, n>0, a(0)=1.
D-finite with recurrence 2*n*(n-2)*(2*n+1)*(n+2)*a(n) -3*(n-1)*(n+3)*(3*n-4)*(3*n-2)*a(n-1)=0. - R. J. Mathar, Mar 12 2017
MATHEMATICA
Join[{0}, Table[(n - 1) Binomial[3 n - 2, n]/(2 n - 1) + (n + 1)Binomial[3 n, n]/(2 n + 1) - Binomial[3 n - 1, n], {n, 30}]] (* Vincenzo Librandi, Sep 28 2015 *)
PROG
(Maxima)
A(x):=x*(2/sqrt(3*x))*sin((1/3)*asin(sqrt(27*x/4)));
taylor(diff(A(x), x, 1)*(1-x/A(x))^2, x, 0, 20);
(Magma) [0] cat [(n-1)*Binomial(3*n-2, n)/(2*n-1)+(n+1)*Binomial(3*n, n)/(2*n+1)-Binomial(3*n-1, n): n in [1..30]]; // Vincenzo Librandi, Sep 28 2015
(PARI) a(n) = (n-1)*binomial(3*n-2, n)/(2*n-1)+(n+1)*binomial(3*n, n)/(2*n+1)-binomial(3*n-1, n);
vector(50, n, a(n-1)) \\ Altug Alkan, Sep 28 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vladimir Kruchinin, Sep 28 2015
STATUS
approved