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Search: id:A161345
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| A161345 |
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Numbers n such that their largest divisor <=sqrt(n) equals 3. |
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37
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| 9, 12, 15, 18, 21, 27, 33, 39, 51, 57, 69, 87, 93, 111, 123, 129, 141, 159, 177, 183, 201, 213, 219, 237, 249, 267, 291, 303, 309, 321, 327, 339, 381, 393, 411, 417, 447, 453, 471, 489, 501, 519, 537, 543, 573, 579, 591, 597, 633, 669, 681, 687, 699, 717, 723
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Define a sieve operation with parameter s that eliminates integers of the form s^2+s*i (i>=0) from the set A000027 of natural numbers. The sequence lists those natural numbers that are eliminated by the sieve s=3 and cannot be eliminated by any sieve s>=4. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 24 2009]
See A161344 for more information. [From Omar E. Pol (info(AT)polprimos.com), Jul 05 2009]
See also the array in A163280, the main entry for this sequence. [From Omar E. Pol (info(AT)polprimos.com), Oct 24 2009]
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LINKS
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O. E. Pol, Determinacion geometrica de los numeros primos y perfectos
O. E. Pol, Illustration: Divisors and pi(x)
O. E. Pol, Illustration for A008578, A161344, A161345 and A161424 [From Omar E. Pol (info(AT)polprimos.com), Oct 24 2009]
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FORMULA
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Numbers n such that A033676(n)=3. [From Omar E. Pol (info(AT)polprimos.com), Jul 05 2009]
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MAPLE
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isA := proc(n, s) if n mod s <> 0 then RETURN(false); fi; if n/s-s >= 0 then RETURN(true); else RETURN(false); fi; end: isA161345 := proc(n) for s from 4 to n do if isA(n, s) then RETURN(false); fi; od: isA(n, 3) ; end: for n from 1 to 3000 do if isA161345(n) then printf("%d, ", n) ; fi; od; [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 24 2009]
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CROSSREFS
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Cf. A000005, A018253, A160811, A160812, A161203, A161204, A161205, A161344, A161346.
Cf. A033676, A008578, A161424, A161835, A162526, A162527, A162528, A162529, A162530, A162531, A162532. [From Omar E. Pol (info(AT)polprimos.com), Jul 05 2009]
Cf. Third column of the array in A163280. Also, third row of array in A163990. [From Omar E. Pol (info(AT)polprimos.com), Oct 24 2009]
Sequence in context: A153044 A138945 A119486 this_sequence A102655 A120167 A048699
Adjacent sequences: A161342 A161343 A161344 this_sequence A161346 A161347 A161348
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KEYWORD
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easy,nonn
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AUTHOR
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Omar E. Pol (info(AT)polprimos.com), Jun 20 2009
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EXTENSIONS
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Terms beyond a(10) from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 24 2009
Definition added by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 28 2009
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