%I A068060
%S A068060 1,2,4,7,14,28,50,100,200,360,720,1440,2560,5120,10240,17920,35840,
%T A068060 71680,130816,261632,523264,915712,1831424,3662848,6516608,13033216,
%U A068060 26066432,46688768,93377536,186755072,333491200,666982400,1333964800
%N A068060 Number of subsets of {1, 2, ..., n} that do not contain a subset of the 
               form {x, 2x, 3x}.
%C A068060 Such subsets are called weakly triple-free sets. A050295 is the strongly 
               triple-free analog of this sequence. [From S. R. Finch (Steven.Finch(AT)inria.fr), 
               Mar 02 2009]
%H A068060 S. R. Finch, <a href="http://algo.inria.fr/csolve/triple/">Triple-Free 
               Sets of Integers</a>
%e A068060 a(6) = 50. There are 64 subsets of {1, 2, 3, 4, 5, 6}. We exclude the 
               8 that contain {1, 2, 3} and the 8 that contain {2, 4, 6}. We've 
               double-counted the 2 that contain {1, 2, 3, 4, 6}. This yields 64 
               - 8 - 8 + 2 = 50.
%Y A068060 Cf. A050293.
%Y A068060 Sequence in context: A018692 A161713 A018330 this_sequence A057744 A113405 
               A119340
%Y A068060 Adjacent sequences: A068057 A068058 A068059 this_sequence A068061 A068062 
               A068063
%K A068060 easy,nonn
%O A068060 0,2
%A A068060 David Wasserman (wasserma(AT)spawar.navy.mil), Feb 14 2002