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A033849 Numbers whose prime factors are 3 and 5. 27
15, 45, 75, 135, 225, 375, 405, 675, 1125, 1215, 1875, 2025, 3375, 3645, 5625, 6075, 9375, 10125, 10935, 16875, 18225, 28125, 30375, 32805, 46875, 50625, 54675, 84375, 91125, 98415, 140625, 151875, 164025, 234375, 253125, 273375, 295245 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Numbers k such that phi(k) = (8/15)*k. - Benoit Cloitre, Apr 19 2002
Subsequence of A143202. - Reinhard Zumkeller, Sep 13 2011
LINKS
FORMULA
From Reinhard Zumkeller, Sep 13 2011: (Start)
A143201(a(n)) = 3.
a(n) = 15*A003593(n). (End)
Sum_{n>=1} 1/a(n) = 1/8. - Amiram Eldar, Dec 22 2020
MATHEMATICA
Sort[Flatten[Table[Table[3^j*5^k, {j, 1, 10}], {k, 1, 10}]]] (* Geoffrey Critzer, Dec 07 2014 *)
Select[Range[300000], FactorInteger[#][[All, 1]]=={3, 5}&] (* Harvey P. Dale, Oct 19 2022 *)
PROG
(Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a033849 n = a033849_list !! (n-1)
a033849_list = f (singleton (3*5)) where
f s = m : f (insert (3*m) $ insert (5*m) s') where
(m, s') = deleteFindMin s
-- Reinhard Zumkeller, Sep 13 2011
CROSSREFS
Subsequence of A256617.
Sequence in context: A298462 A066763 A164788 * A194715 A060536 A014634
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset and typo in data fixed by Reinhard Zumkeller, Sep 13 2011
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)