

A135060


a(n) = smallest number m for which none of the first n multiples of m has twice as many divisors as m.


5



1, 2, 6, 12, 60, 120, 840, 840, 2520, 2520, 27720, 55440, 720720, 720720, 1081080, 2162160, 36756720, 36756720, 698377680, 698377680, 698377680, 698377680, 16062686640, 48188059920, 160626866400, 160626866400, 160626866400
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OFFSET

1,2


COMMENTS

a(n) is smallest value m where A129902(m)/m > n.
Conjecture: every number in this sequence is also in A002182.  Lowell Disproved at a(24) = 48188059920  Chandler.
The conjecture that every term is a multiple of the preceding term is disproved at n = 15; a(15) = 1081080, which is not a multiple of 720720.  J. Lowell, Jun 06 2008


LINKS

Ray Chandler, Table of n, a(n) for n=1..130


EXAMPLE

60 does not qualify for a(6) because 60 has 12 divisors and 60*6=360 has 12*2=24 divisors.


CROSSREFS

Sequence in context: A263572 A004490 A224078 * A185021 A191836 A072486
Adjacent sequences: A135057 A135058 A135059 * A135061 A135062 A135063


KEYWORD

nonn


AUTHOR

J. Lowell, Feb 11 2008, Jul 08 2008, Jul 14 2008


EXTENSIONS

More terms from J. Lowell, May 13 2009
Corrected inequality in the comment and added a(16)  R. J. Mathar, Nov 04 2009
Extended by Ray Chandler, Nov 10 2009


STATUS

approved



