A181657 Generalized (conditional) Riordan array with k-th column generated by x^k * (1 + x - x^2 + x^3)/(1 - 2x^2 - x^4) if k mod 2 = 0, x^k * (1+x)/(1 - 2x^2 - x^4) otherwise.

1, 1, 1, 1, 1, 1, 3, 2, 1, 1, 3, 2, 1, 1, 1, 7, 5, 3, 2, 1, 1, 7, 5, 3, 2, 1, 1, 1, 17, 12, 7, 5, 3, 2, 1, 1, 17, 12, 7, 5, 3, 2, 1, 1, 1, 41, 29, 17, 12, 7, 5, 3, 2, 1, 1, 41, 29, 17, 12, 7, 5, 3, 2, 1, 1, 1

Offset: 0

Author

Paul Barry, Nov 03 2010

Keywords

• easy
• nonn
• tabl

Comments

An eigentriangle of A181656. Even columns are essentially A001333 doubled. Odd columns are doubled Pell numbers (A000129).

Row sums are A181658.

Examples

			Triangle begins
   1;
   1,  1;
   1,  1,  1;
   3,  2,  1,  1;
   3,  2,  1,  1,  1;
   7,  5,  3,  2,  1,  1;
   7,  5,  3,  2,  1,  1,  1;
  17, 12,  7,  5,  3,  2,  1,  1;
  17, 12,  7,  5,  3,  2,  1,  1,  1;
  41, 29, 17, 12,  7,  5,  3,  2,  1,  1;
  41, 29, 17, 12,  7,  5,  3,  2,  1,  1,  1;