A033848 - OEIS

%I #36 Feb 16 2024 10:20:17

%S 22,44,88,176,242,352,484,704,968,1408,1936,2662,2816,3872,5324,5632,

%T 7744,10648,11264,15488,21296,22528,29282,30976,42592,45056,58564,

%U 61952,85184,90112,117128,123904,170368,180224,234256,247808,322102

%N Numbers whose prime factors are 2 and 11.

%C Numbers k such that phi(k)/k = 5/11. - _Michel Marcus_, Sep 22 2012

%H Reinhard Zumkeller, <a href="/A033848/b033848.txt">Table of n, a(n) for n = 1..10000</a>

%F A143201(a(n)) = 10. - _Reinhard Zumkeller_, Sep 13 2011

%F Sum_{n>=1} 1/a(n) = 1/10. - _Amiram Eldar_, Dec 22 2020

%p N:= 10^6: # to get all terms <= N

%p S:= {seq(seq(2^i*11^j, i=1..ilog2(floor(N/11^j))),j=1..floor(log[11](N/2)))}:

%p sort(convert(S,list)); # _Robert Israel_, Oct 26 2017

%t Select[Range[10^6], FactorInteger[#][[All, 1]] == {2, 11} &] (* _Michael De Vlieger_, Oct 26 2017 *)

%t Sort[Flatten[Table[Table[2^j 11^k, {j, 1, 8}], {k, 1, 8}]]] (* _Vincenzo Librandi_, Oct 27 2017 *)

%o (Haskell)

%o import Data.Set (singleton, deleteFindMin, insert)

%o a033848 n = a033848_list !! (n-1)

%o a033848_list = f (singleton (2*11)) where

%o    f s = m : f (insert (2*m) $ insert (11*m) s') where

%o      (m,s') = deleteFindMin s

%o -- _Reinhard Zumkeller_, Sep 13 2011

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

%K nonn

%O 1,1

%A _Jeff Burch_