A026127 a(n) = T(2n-1,n-1), where T is the array in A026120.

1, 4, 20, 110, 608, 3409, 19304, 110187, 632960, 3654915, 21195716, 123365099, 720240584, 4216176575, 24738092400, 145444454754, 856662911136, 5053815390148, 29857490333880, 176624209891024

Offset

1,2

Links

Table of n, a(n) for n=1..20.

Prog

(PARI)
A026300(n, k)={ if(n<0 || k < 0, return(0) ; ) ; if(n<=1, 1, if(k==0, 1, sum(i=0, k/2, binomial(n, 2*i+n-k)*(binomial(2*i+n-k, i)-binomial(2*i+n-k, i-1))) ; ) ; ) ; }
A026105(n, k)={ if(k==0 || n<=1, 1, A026300(n, k)-A026300(n-1, k-1) ; ) ; }
A026120(n, k)={ if(n<=1, if(k== -1 || k < n, 1, 0), A026105(n+1, k+1)-A026105(n, k) ; ) ; }
A026127(n)={ A026120(2*n-1, n-1) ; }
{ vector(20, n, A026127(n)) } \\ R. J. Mathar, Dec 06 2006

Crossrefs

Sequence in context: A225621 A020084 A325956 * A222205 A262394 A271932

Adjacent sequences: A026124 A026125 A026126 * A026128 A026129 A026130

Keyword

nonn

Author

Clark Kimberling

Extensions

Corrected by R. J. Mathar, Oct 26 2006

Status

approved