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

1,1

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.

Links

Table of n, a(n) for n=1..72.

Example

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.

Sequence in context: A334595 A350684 A124443 * A160047 A249990 A097288

Adjacent sequences: A077169 A077170 A077171 * A077173 A077174 A077175

Keyword

nonn,tabl

Author

Amarnath Murthy, Nov 01 2002

Extensions

Extended by Ray Chandler, Nov 29 2004

Status

approved