A376811 Expansion of 1/sqrt(1 - 4*x/(1 - x^3)^2).

1, 2, 6, 20, 74, 276, 1044, 3998, 15450, 60128, 235332, 925332, 3652508, 14464490, 57442074, 228670140, 912239782, 3646027752, 14596600800, 58523194734, 234954663396, 944418233612, 3800327339532, 15307785490560, 61716607166724, 249033637247898, 1005661821858414

Offset: 0

Author

Seiichi Manyama, Oct 04 2024

Keywords

• nonn

Crossrefs

Cf. A110170, A376810.

Cf. A376791.

Programs

PARI

my(N=30, x='x+O('x^N)); Vec(1/sqrt(1-4*x/(1-x^3)^2))

PARI

a(n) = sum(k=0, n\3, binomial(2*n-5*k-1, k)*binomial(2*n-6*k, n-3*k));

Formula

a(n) = Sum_{k=0..floor(n/3)} binomial(2*n-5*k-1,k) * binomial(2*n-6*k,n-3*k).