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A033850
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Numbers n whose prime factors are 3 and 7.
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10
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21, 63, 147, 189, 441, 567, 1029, 1323, 1701, 3087, 3969, 5103, 7203, 9261, 11907, 15309, 21609, 27783, 35721, 45927, 50421, 64827, 83349, 107163, 137781, 151263, 194481, 250047, 321489, 352947, 413343, 453789, 583443, 750141, 964467
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Also, numbers n such that phi(n)/n = 4/7, where phi is the Euler totient function A000010. - Lekraj Beedassy (blekraj(AT)yahoo.com), Jul 18 2008
A143201(a(n)) = 5; subsequence of A143203. [Reinhard Zumkeller, Sep 13 2011]
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REFERENCES
| J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 189, p. 57, Ellipses, Paris 2008.
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LINKS
| Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
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PROG
| (Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a033850 n = a033850_list !! (n-1)
a033850_list = f (singleton (3*7)) where
f s = m : f (insert (3*m) $ insert (7*m) s') where
(m, s') = deleteFindMin s
-- Reinhard Zumkeller, Sep 13 2011
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CROSSREFS
| Cf. A033845, A033846, A033847, A033848, A033849, A033851.
Sequence in context: A143203 A082060 A025525 * A170930 A113622 A069215
Adjacent sequences: A033847 A033848 A033849 * A033851 A033852 A033853
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KEYWORD
| nonn
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AUTHOR
| Jeff Burch (gburch(AT)erols.com)
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EXTENSIONS
| Offset fixed by Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 13 2011
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