A024720 a(n) = (1/4)*(3 + Sum_{k=0..n} C(4k,k)).

1, 2, 9, 64, 519, 4395, 38044, 334054, 2963629, 26499449, 238414581, 2155749364, 19572882981, 178326272881, 1629509263831, 14928031562011, 137059765831906, 1260847661188318, 11618870102584178, 107234108018545278

Offset

0,2

Links

Table of n, a(n) for n=0..19.

Formula

G.f.: (2*g-3)*g^4/((3*g-4)*(1-g+g^4)) where g = 1+x*g^4 is the g.f. of A002293. - Mark van Hoeij, Nov 11 2011

Prog

(PARI) a(n) = (3+sum(k=0, n, binomial(4*k, k)))/4; \\ Michel Marcus, May 10 2020

Crossrefs

Cf. A002293.

Sequence in context: A074181 A052513 A216839 * A289717 A094100 A185897

Adjacent sequences: A024717 A024718 A024719 * A024721 A024722 A024723

Keyword

nonn

Author

Clark Kimberling

Extensions

More terms from James A. Sellers, May 01 2000

Status

approved