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

0,4

Comments

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

Links

Table of n, a(n) for n=0..57.

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

Example

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

Crossrefs

Sequence in context: A296541 A056152 A171229 * A176481 A108553 A176700

Adjacent sequences: A125687 A125688 A125689 * A125691 A125692 A125693

Keyword

easy,nonn,tabl

Author

Paul Barry, Nov 30 2006

Status

approved