A124279 Riordan array (1/(1-x),x(1-x+x^2)/(1-x)).

1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 3, 3, 1, 1, 1, 4, 5, 4, 1, 1, 1, 5, 8, 7, 5, 1, 1, 1, 6, 12, 13, 9, 6, 1, 1, 1, 7, 17, 22, 19, 11, 7, 1, 1, 1, 8, 23, 35, 35, 26, 13, 8, 1, 1, 1, 9, 30, 53

Offset

0,8

Comments

Row sums are A005314. Diagonal sums are A124280. T(2n,n) is A002426.

Reversal of A124445. - Paul Barry, Nov 01 2006

Links

Table of n, a(n) for n=0..58.

Formula

Number triangle T(n,k)=sum{j=0..n-k, C(j,n-k-j)C(k,n-k-j)}

Example

Triangle begins
1,
1, 1,
1, 1, 1,
1, 2, 1, 1,
1, 3, 3, 1, 1,
1, 4, 5, 4, 1, 1,
1, 5, 8, 7, 5, 1, 1

Crossrefs

Sequence in context: A096815 A193516 A124445 * A297299 A135225 A208891

Adjacent sequences: A124276 A124277 A124278 * A124280 A124281 A124282

Keyword

easy,nonn,tabl

Author

Paul Barry, Oct 24 2006

Status

approved