cp's OEIS Frontend

A033848 Numbers whose prime factors are 2 and 11.

%I A033848 #36 Feb 16 2024 10:20:17
%S A033848 22,44,88,176,242,352,484,704,968,1408,1936,2662,2816,3872,5324,5632,
%T A033848 7744,10648,11264,15488,21296,22528,29282,30976,42592,45056,58564,
%U A033848 61952,85184,90112,117128,123904,170368,180224,234256,247808,322102
%N A033848 Numbers whose prime factors are 2 and 11.
%C A033848 Numbers k such that phi(k)/k = 5/11. - _Michel Marcus_, Sep 22 2012
%H A033848 Reinhard Zumkeller, <a href="/A033848/b033848.txt">Table of n, a(n) for n = 1..10000</a>
%F A033848 A143201(a(n)) = 10. - _Reinhard Zumkeller_, Sep 13 2011
%F A033848 Sum_{n>=1} 1/a(n) = 1/10. - _Amiram Eldar_, Dec 22 2020
%p A033848 N:= 10^6: # to get all terms <= N
%p A033848 S:= {seq(seq(2^i*11^j, i=1..ilog2(floor(N/11^j))),j=1..floor(log[11](N/2)))}:
%p A033848 sort(convert(S,list)); # _Robert Israel_, Oct 26 2017
%t A033848 Select[Range[10^6], FactorInteger[#][[All, 1]] == {2, 11} &] (* _Michael De Vlieger_, Oct 26 2017 *)
%t A033848 Sort[Flatten[Table[Table[2^j 11^k, {j, 1, 8}], {k, 1, 8}]]] (* _Vincenzo Librandi_, Oct 27 2017 *)
%o A033848 (Haskell)
%o A033848 import Data.Set (singleton, deleteFindMin, insert)
%o A033848 a033848 n = a033848_list !! (n-1)
%o A033848 a033848_list = f (singleton (2*11)) where
%o A033848    f s = m : f (insert (2*m) $ insert (11*m) s') where
%o A033848      (m,s') = deleteFindMin s
%o A033848 -- _Reinhard Zumkeller_, Sep 13 2011
%Y A033848 Cf. A033845, A033846, A033847, A033849, A033850, A033851, A143201.
%K A033848 nonn
%O A033848 1,1
%A A033848 _Jeff Burch_