This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A068060 Number of subsets of {1, 2, ..., n} that do not contain a subset of the form {x, 2x, 3x}. 2
 1, 2, 4, 7, 14, 28, 50, 100, 200, 360, 720, 1440, 2560, 5120, 10240, 17920, 35840, 71680, 130816, 261632, 523264, 915712, 1831424, 3662848, 6516608, 13033216, 26066432, 46688768, 93377536, 186755072, 333491200, 666982400, 1333964800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Such subsets are called weakly triple-free sets. A050295 is the strongly triple-free analog of this sequence. [From Steven Finch, Mar 02 2009] LINKS S. R. Finch, Triple-Free Sets of Integers EXAMPLE 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. CROSSREFS Cf. A050293. Sequence in context: A018692 A161713 A018330 * A057744 A210210 A113405 Adjacent sequences:  A068057 A068058 A068059 * A068061 A068062 A068063 KEYWORD easy,nonn AUTHOR David Wasserman, Feb 14 2002 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified May 22 01:14 EDT 2013. Contains 225508 sequences.