A131413 Triangle read by rows: A002024 + A128076 - A000012 as infinite lower triangular matrices.

1, 4, 3, 7, 6, 5, 10, 9, 8, 7, 13, 12, 11, 10, 9, 16, 15, 14, 13, 12, 11, 19, 18, 17, 16, 15, 14, 13, 22, 21, 20, 19, 18, 17, 16, 15, 25, 24, 23, 22, 21, 20, 19, 18, 17, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23

Offset: 0

Author

Gary W. Adamson, Jul 08 2007

Keywords

• nonn
• tabl

Comments

Row sums = A000566, the heptagonal numbers: (1, 7, 18, 34, 55, ...).

Examples

			First few rows of the triangle:
   1;
   4,  3;
   7,  6,  5;
  10,  9,  8,  7;
  13, 12, 11, 10,  9;
  16, 15, 14, 13, 12, 11;
  19, 18, 17, 16, 15, 14, 13;
  ...
		

Crossrefs

Cf. A000566, A002024, A128076.

Formula

By rows, (n+1) terms of 3n+1, 3n, 3n-1, ...

Extensions

a(5) = 5, a(30) = 20 corrected and more terms from Georg Fischer, Jun 07 2023