A181654 An eigentriangle of the number triangle A181653.

1, 1, 1, 2, 1, 1, 3, 2, 1, 1, 6, 4, 2, 1, 1, 9, 6, 3, 2, 1, 1, 18, 12, 6, 4, 2, 1, 1, 27, 18, 9, 6, 3, 2, 1, 1, 54, 36, 18, 12, 6, 4, 2, 1, 1, 81, 54, 27, 18, 9, 6, 3, 2, 1, 1, 162, 108, 54, 36, 18, 12, 6, 4, 2, 1, 1

Offset: 0

Author

Paul Barry, Nov 03 2010

Keywords

• easy
• nonn
• tabl

Comments

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

Row sums are A181655.

Examples

			Triangle begins
1,
1, 1,
2, 1, 1,
3, 2, 1, 1,
6, 4, 2, 1, 1,
9, 6, 3, 2, 1, 1,
18, 12, 6, 4, 2, 1, 1,
27, 18, 9, 6, 3, 2, 1, 1,
54, 36, 18, 12, 6, 4, 2, 1, 1,
81, 54, 27, 18, 9, 6, 3, 2, 1, 1,
162, 108, 54, 36, 18, 12, 6, 4, 2, 1, 1
		

Links

• Paul Barry, Invariant number triangles, eigentriangles and Somos-4 sequences, arXiv preprint arXiv:1107.5490 [math.CO], 2011.