OFFSET
2,3
LINKS
FORMULA
a(n) = 7*(n-1)*binomial(3n-6, n-4)/(2n-1).
G.f.: g^2*(2*g-3)/((1-3*g)*(g-1)^3) where g*(1-g)^2 = x. - Mark van Hoeij, Nov 10 2011
a(n) = Sum_{k=0..ceiling(n/2)-1} k*A101431(n, k). - Andrew Howroyd, Nov 17 2017
D-finite with recurrence +2*(2*n-1)*(n-4)*a(n) -3*(3*n-7)*(3*n-8)*a(n-1)=0. - R. J. Mathar, Jul 26 2022
MATHEMATICA
Table[7(n-1) Binomial[3n-6, n-4]/(2n-1), {n, 2, 30}] (* Harvey P. Dale, Nov 01 2017 *)
PROG
(PARI) a(n) = 7*(n-1)*binomial(3*n-6, n-4)/(2*n-1); \\ Andrew Howroyd, Nov 11 2017
(PARI) \\ here b(n) is x^2 * g.f. of A006013.
b(n)=serreverse(x - 2*x^2 + x^3 + O(x^n));
s(n)={(g->g^2*(2*g-3)/((1-3*g)*(g-1)^3))(b(n)) + O(x^n)}
concat([0, 0], Vec(s(25))) \\ Andrew Howroyd, Nov 11 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved