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

Author

Paul Barry, Oct 24 2006

Keywords

• easy
• nonn
• tabl

Comments

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

Reversal of A124445. - Paul Barry, Nov 01 2006

Examples

			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
		

Formula

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