A065221 Fill a triangular array by rows by writing numbers 1 up to b(0), 1 up to b(1), etc., where b(n) are the pentagonal numbers. The final elements of the rows form a(n).

1, 2, 5, 4, 9, 3, 10, 18, 5, 15, 26, 3, 16, 30, 45, 10, 27, 45, 64, 14, 35, 57, 80, 12, 37, 63, 90, 1, 30, 60, 91, 123, 11, 45, 80, 116, 153, 15, 54, 94, 135, 177, 10, 54, 99, 145, 192, 240, 42, 92, 143, 195, 248, 15, 70, 126, 183, 241, 300, 30, 91, 153, 216, 280, 345, 35

Offset: 0

Author

Floor van Lamoen, Oct 22 2001

Keywords

• easy
• nonn

Examples

			The array begins
....1
...1.2
..3.4.5
.1.2.3.4
5.6.7.8.9
		

Crossrefs

Cf. A000326.

Mini-index to these sequences: A064766, A064865, A064866, A065221-A655234 are all of the same type. See A064766 for a detailed explanation.