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A072567
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Size of maximal set of points in an n X n (side length) grid such that no 4-set of it forms a rectangle with horizontal/vertical sides.
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0
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1, 3, 6, 9, 12, 16, 21, 24, 29, 34, 39, 45, 52
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Finding a(7) is presented as a puzzle in Mathematical Gems III by Ross Honsberger on page 4. - Tanya Khovanova (tanyakh(AT)yahoo.com), Oct 12 2007
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EXAMPLE
| Examples for n=1 and n=2:
*-*....*-*-O
|.|....|.|.|
*-O....*-O-*
.......|.|.|
.......O-*-*
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CROSSREFS
| Sequence in context: A130248 A203302 A194199 * A186353 A061796 A113241
Adjacent sequences: A072564 A072565 A072566 * A072568 A072569 A072570
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KEYWORD
| nonn,nice
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AUTHOR
| Xuli Le (leshlie(AT)eyou.com), Jun 21 2002
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EXTENSIONS
| a(1) = 1 from Don Reble, Oct 13 2007
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