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A140286 The n-th lucky number which is the product of exactly n primes (with multiplicity). 0
3, 15, 99, 495, 2079, 4455, 36855, 70875, 280665, 1393119, 4179357, 12931731, 32417901, 161026623, 514966329, 1490692005 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is the main diagonal of the infinite array A(k,n) = n-th n-th lucky number to be the product of exactly k primes, with multiplicity, which begins as below:

============================================================================

k |  n=1 |  n=2 |  n=3 |  n=4 |  n=5 |  n=6 |  n=7 |  n=8 |   n=9 |  n=10 |in OEIS

1 |    3 |   7  |  13  |  31  |  37  |  43  |  67  |  73  |   79  |  127  |A031157

2 |    9 |  15  |  21  |  25  |  33  |  49  |  51  |  69  |   87  |   93  |A139787

3 |   63 |  75  |  99  | 105  | 171  | 195  | 231  | 261  |  273  |  285  |

4 |  297 | 495  | 621  | 693  | 735  | 819  | 855  | 975  | 1029  | 1107  |

5 | 1053 |                                                                |

6 |  729 |                                                                |

============================================================================

a(16) > 10^9. - Donovan Johnson, Oct 24 2010

LINKS

Table of n, a(n) for n=1..16.

EXAMPLE

a(4) = 693 because the 113th lucky number = 693 = 3^2 * 7 * 11 is the 4th lucky number with 4 prime factors.

CROSSREFS

Cf. A000040, A000959, A001358, A014612, A031157, A139787.

Sequence in context: A331618 A128081 A186264 * A199416 A046635 A208426

Adjacent sequences:  A140283 A140284 A140285 * A140287 A140288 A140289

KEYWORD

nonn,more,less

AUTHOR

Jonathan Vos Post, May 24 2008

EXTENSIONS

a(4) corrected and 5 more terms via b000959.txt from R. J. Mathar, Oct 22 2010

a(10)-a(15) from Donovan Johnson, Oct 24 2010

a(16) from Giovanni Resta, May 10 2020

STATUS

approved

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Last modified August 6 12:33 EDT 2020. Contains 336246 sequences. (Running on oeis4.)