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A077172 Triangle formed by grouping the natural numbers so that the n-th row contains n numbers whose product has exactly n prime divisors. 6
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 (list; table; graph; refs; listen; history; text; internal format)
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
EXAMPLE
2;
1,6;
3,4,5;
7,8,9,10;
11,12,13,14,16;
15,17,18,19,20,21;
...
CROSSREFS
Sequence in context: A334595 A350684 A124443 * A160047 A249990 A097288
KEYWORD
nonn,tabl
AUTHOR
Amarnath Murthy, Nov 01 2002
EXTENSIONS
Extended by Ray Chandler, Nov 29 2004
STATUS
approved

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Last modified June 24 02:53 EDT 2024. Contains 373661 sequences. (Running on oeis4.)