A122431 Riordan array ((1+x)^3,x).

1, 3, 1, 3, 3, 1, 1, 3, 3, 1, 0, 1, 3, 3, 1, 0, 0, 1, 3, 3, 1, 0, 0, 0, 1, 3, 3, 1, 0, 0, 0, 0, 1, 3, 3, 1, 0, 0, 0, 0, 0, 1, 3, 3, 1, 0, 0, 0, 0, 0, 0, 1, 3, 3, 1, 0, 0, 0, 0, 0, 0, 0, 1

Offset: 0

Author

Paul Barry, Sep 04 2006

Keywords

• easy
• nonn
• tabl

Comments

Row sums are A115291. Diagonal sums are A113311. Inverse is A122432. Sequence array for C(3,n).

Examples

			Triangle begins
1,
3,1,
3,3,1,
1,3,3,1,
0,1,3,3,1,
0,0,1,3,3,1,
0,0,0,1,3,3,1,
0,0,0,0,1,3,3,1
		

Formula

Number triangle T(n,k)=C(3,n-k)