A077172 Triangle formed by grouping the natural numbers so that the n-th row contains n numbers whose product has exactly n distinct prime divisors.

2, 1, 6, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 16, 15, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 48, 44, 46, 47, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72

Offset: 1

Author

Amarnath Murthy, Nov 01 2002

Keywords

• nonn
• tabl

Comments

Next available unused natural number is added to n-th row unless it would cause product for that row to exceed n prime divisors.

Examples

			2;
1,6;
3,4,5;
7,8,9,10;
11,12,13,14,16;
15,17,18,19,20,21;
...
		

Crossrefs

Cf. A077173, A077174, A077175, A077176, A100918.

Extensions

Extended by Ray Chandler, Nov 29 2004