A117381 Expansion of 1/((1-4*x*c(x))(1-x^2*c(x))), c(x) the g.f. of A000108.

1, 4, 21, 109, 575, 3047, 16192, 86171, 458972, 2445825, 13037508, 69509558, 370634265, 1976421031, 10539858413, 56208784808, 299766435277, 1598704176149, 8526238418811, 45472594256564, 242517996824355

Offset

0,2

Comments

Diagonal sums of number triangle A117380.

Links

Table of n, a(n) for n=0..20.

Formula

a(n)=sum{k=0..floor(n/2), [k<=n-k]*sum{j=0..n-k, (j/(n-k-j))*C(2n-k-j,n-k-j)[k<=j]*4^(j-k)}}

Crossrefs

Sequence in context: A377111 A183367 A100237 * A010908 A136786 A301972

Adjacent sequences: A117378 A117379 A117380 * A117382 A117383 A117384

Keyword

easy,nonn

Author

Paul Barry, Mar 10 2006

Status

approved