A125690 Riordan array (1/(1-x-2x^2), x(1-x)/(1-x-2x^2)).

1, 1, 1, 3, 1, 1, 5, 5, 1, 1, 11, 9, 7, 1, 1, 21, 25, 13, 9, 1, 1, 43, 53, 43, 17, 11, 1, 1, 85, 125, 97, 65, 21, 13, 1, 1, 171, 273, 255, 153, 91, 25, 15, 1, 1, 341, 609, 597, 441, 221, 121, 29, 17, 1, 1, 683, 1325, 1443

Offset: 0

Author

Paul Barry, Nov 30 2006

Keywords

• easy
• nonn
• tabl

Comments

First column is A001045. Row sums are Pell numbers A000129(n+1). Diagonal sums are A125691.

Examples

			Triangle begins
1,
1, 1,
3, 1, 1,
5, 5, 1, 1,
11, 9, 7, 1, 1,
21, 25, 13, 9, 1, 1,
43, 53, 43, 17, 11, 1, 1
		

Formula

G.f.: 1/(1-x-2x^2-xy(1-x)).

T(n,k) = T(n-1,k) + T(n-1,k-1) + 2*T(n-2,k) - T(n-2,k-1). - Philippe Deléham, Feb 24 2012