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

Author

Clark Kimberling

Keywords

• nonn

Examples

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

Programs

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 */

Formula

G.f.: A(x) = (1/B(x))'-1, where B(x) is the 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