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A057561
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A density problem involving linear forms.
(Formerly M0949)
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4
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1, 2, 2, 3, 4, 5, 5, 6, 7, 7, 8, 8, 9, 10, 11, 11, 12, 13, 13, 14, 14, 15, 16, 17, 17, 18, 18, 19, 20, 20, 21, 22, 22, 23, 24, 25
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| A094708(n) = n - a(n)
Position of first n gives A004059(n).
Contribution from S. R. Finch (Steven.Finch(AT)inria.fr), Feb 27 2009: (Start)
Size of the largest set encompassing no {x, 2x, 3x} contained in D(n) = the first n 3-smooth numbers {1, 2, 3, 4, 6, 8, 9, 12, 16, 18, 24, 27,...} (A003586).
This is the weakly triple-free analog of A157271. (End)
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REFERENCES
| R. L. Graham et al., On extremal density theorems for linear forms, pp. 103-109 of H. Zassenhaus, editor, Number Theory and Algebra. Academic Press, NY, 1977.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| S. R. Finch, Triple-Free Sets of Integers
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CROSSREFS
| Cf. A004059, A094708.
Sequence in context: A065855 A034137 A156351 * A064726 A057359 A076538
Adjacent sequences: A057558 A057559 A057560 * A057562 A057563 A057564
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Edited by S. R. Finch (Steven.Finch(AT)inria.fr), Feb 25 2009
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