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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 24 14:36 EDT 2019. Contains 326285 sequences. (Running on oeis4.)