A033848 Numbers whose prime factors are 2 and 11.

22, 44, 88, 176, 242, 352, 484, 704, 968, 1408, 1936, 2662, 2816, 3872, 5324, 5632, 7744, 10648, 11264, 15488, 21296, 22528, 29282, 30976, 42592, 45056, 58564, 61952, 85184, 90112, 117128, 123904, 170368, 180224, 234256, 247808, 322102

Offset: 1

Author

Jeff Burch

Keywords

• nonn

Comments

Numbers k such that phi(k)/k = 5/11. - Michel Marcus, Sep 22 2012

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A033845, A033846, A033847, A033849, A033850, A033851, A143201.

Programs

Haskell

import Data.Set (singleton, deleteFindMin, insert)
a033848 n = a033848_list !! (n-1)
a033848_list = f (singleton (2*11)) where
   f s = m : f (insert (2*m) $ insert (11*m) s') where
     (m,s') = deleteFindMin s
-- Reinhard Zumkeller, Sep 13 2011

Maple

N:= 10^6: # to get all terms <= N
S:= {seq(seq(2^i*11^j, i=1..ilog2(floor(N/11^j))),j=1..floor(log[11](N/2)))}:
sort(convert(S,list)); # Robert Israel, Oct 26 2017

Mathematica

Select[Range[10^6], FactorInteger[#][[All, 1]] == {2, 11} &] (* Michael De Vlieger, Oct 26 2017 *)
Sort[Flatten[Table[Table[2^j 11^k, {j, 1, 8}], {k, 1, 8}]]] (* Vincenzo Librandi, Oct 27 2017 *)

Formula

A143201(a(n)) = 10. - Reinhard Zumkeller, Sep 13 2011

Sum_{n>=1} 1/a(n) = 1/10. - Amiram Eldar, Dec 22 2020