%I A050291
%S A050291 2,3,6,10,20,30,60,96,192,288,576,960,1920,2880,5760,9360,18720,28080,
%T A050291 56160,93600,187200,280800,561600,898560,1797120,2695680,5391360,
%U A050291 8985600,17971200,26956800,53913600,87091200,174182400,261273600
%N A050291 Number of double-free subsets of {1, 2, ..., n}.
%C A050291 A set is double-free if it does not contain both x and 2x.
%D A050291 Wang, E. T. H. ``On Double-Free Sets of Integers.'' Ars Combin. 28, 97-100, 
               1989.
%H A050291 T. D. Noe, <a href="b050291.txt">Table of n, a(n) for n=1..400</a>
%H A050291 S. R. Finch, <a href="http://algo.inria.fr/csolve/triple/">Triple-Free 
               Sets of Integers</a>
%H A050291 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Double-FreeSet.html">Link to a section of The World of Mathematics.</
               a>
%F A050291 a(n+1)=a(n)*Fib(b(2n)+2)/Fib(b(2n)+1), Fib = A000045, b = A007814.
%F A050291 a(n) = 2^n - A088808(n). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), 
               Oct 19 2003
%Y A050291 Cf. A050292-A050296.
%Y A050291 Sequence in context: A005833 A001678 A113292 this_sequence A135452 A077027 
               A030436
%Y A050291 Adjacent sequences: A050288 A050289 A050290 this_sequence A050292 A050293 
               A050294
%K A050291 nonn,easy,nice
%O A050291 1,1
%A A050291 Eric Weisstein (eric(AT)weisstein.com)
%E A050291 Extended with formula by Christian G. Bower (bowerc(AT)usa.net), Sep 
               15 1999