A026306 a(n) = T(2n,n+1), where T is the array in A026300.

0, 2, 12, 69, 392, 2235, 12804, 73710, 426192, 2473704, 14405800, 84137130, 492652824, 2891110235, 16999928820, 100136858625, 590778928800, 3490370847876, 20647839813048, 122287764072938, 725023671281520, 4302720916638417

Offset

0,2

Links

Table of n, a(n) for n=0..21.

Formula

g.f. A(x)=(1/B(x))'-1, where B(x) g.f. of A006605.

a(n) = n*(Sum_{j=0..2*n+1} binomial(j,-3*n+2*j-1)*binomial(2*n+1,j)))/(2*n+1) - Vladimir Kruchinin, May 15 2014

Example

G.f. = 2*x + 12*x^2 + 69*x^3 + 392*x^4 + 2235*x^5 + 12804*x^6 + 73710*x^7 + ...

Prog

(Maxima)
a(n):=(n*sum(binomial(j, -3*n+2*j-1)*binomial(2*n+1, j), j, 0, 2*n+1))/(2*n+1); Vladimir Kruchinin, May 15 2014

Crossrefs

Sequence in context: A245854 A078839 A243771 * A116398 A001542 A059229

Adjacent sequences: A026303 A026304 A026305 * A026307 A026308 A026309

Keyword

nonn

Author

Clark Kimberling

Status

approved