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A033845
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Numbers n of the form 2^i*3^j, i and j >= 1.
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25
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6, 12, 18, 24, 36, 48, 54, 72, 96, 108, 144, 162, 192, 216, 288, 324, 384, 432, 486, 576, 648, 768, 864, 972, 1152, 1296, 1458, 1536, 1728, 1944, 2304, 2592, 2916, 3072, 3456, 3888, 4374, 4608, 5184, 5832, 6144, 6912, 7776, 8748, 9216, 10368, 11664
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Solutions to phi(n)=n/3.
Numbers n such that sum(d prime divisor of n, 1/d)=5/6 [Benoit Cloitre, Apr 13 2002]
Also n such that sum(d|n,mu(d)^2/d)=2 [Benoit Cloitre, Apr 15 2002]
Complement of A006899 with respect to A003586; A086411(a(n))-A086410(a(n))=1. [From Reinhard Zumkeller, Sep 25 2008]
In the sieve of Eratosthenes, if one crosses numbers off multiple times, these numbers are crossed off twice, first for 2 and then for 3. [From Alonso del Arte, Aug 22 2011]
A143201(a(n)) = 2; subsequence of A051037. [Reinhard Zumkeller, Sep 13 2011]
Numbers n such that sum(d|n, A008683(d)*A000041(d) )=7 - Carl Najafi, Oct 19 2011
Numbers n such that sum(d|n, A008683(d)*A000700(d) )=2 - Carl Najafi, Oct 20 2011
Solutions to the equation A001615(x)=2x. - Enrique Pérez Herrero, Jan 02 2012.
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LINKS
| Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
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MATHEMATICA
| Sort[Flatten[Table[2^i 3^j, {i, 7}, {j, 7}]]] (* From Alonso del Arte, Aug 22 2011 *)
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PROG
| (Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a033845 n = a033845_list !! (n-1)
a033845_list = f (singleton (2*3)) where
f s = m : f (insert (2*m) $ insert (3*m) s') where
(m, s') = deleteFindMin s
-- Reinhard Zumkeller, Sep 13 2011
(PARI) list(lim)=my(v=List(), N); for(n=0, log(lim\2)\log(3), N=6*3^n; while(N<=lim, listput(v, N); N<<=1)); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jan 02 2012
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CROSSREFS
| Six times the 3-smooth numbers (A003586). - R. Stephan, Apr 16 2004
A subsequence of A000423.
Cf. A033846, A033847, A033848, A033849, A033850, A033851.
Sequence in context: A037230 A033018 A189781 * A120942 A147306 A031478
Adjacent sequences: A033842 A033843 A033844 * A033846 A033847 A033848
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KEYWORD
| nonn
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AUTHOR
| Jeff Burch (gburch(AT)erols.com)
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EXTENSIONS
| Minor edits by N. J. A. Sloane, Jan 31 2010.
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