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A161424
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Numbers n such that their largest divisor <= sqrt(n) equals 4.
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24
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16, 20, 24, 28, 32, 44, 52, 68, 76, 92, 116, 124, 148, 164, 172, 188, 212, 236, 244, 268, 284, 292, 316, 332, 356, 388, 404, 412, 428, 436, 452, 508, 524, 548, 556, 596, 604, 628, 652, 668, 692, 716, 724, 764, 772, 788, 796, 844, 892, 908, 916, 932, 956, 964
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 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=4 and cannot be eliminated by any sieve s>=5. [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
| 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
| Numbers n such that A033676(n)=4. [From Omar E. Pol (info(AT)polprimos.com), Jul 05 2009]
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MAPLE
| 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: isA161424 := proc(n) for s from 5 to n do if isA(n, s) then RETURN(false); fi; od: isA(n, 4) ; end: for n from 1 to 3000 do if isA161424(n) then printf("%d, ", n) ; fi; od; [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 24 2009]
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CROSSREFS
| Cf. A000005, A018253, A160811, A160812, A161205, A161344, A161345, A161346, A161425, A161428, A033676, A008578, A161835, A162526, A162527, A162528, A162529, A162530, A162531, A162532.
Cf. Fourth column of array in A163280. Also, fourth row of array in A163990. [From Omar E. Pol (info(AT)polprimos.com), Oct 24 2009]
Sequence in context: A199716 A163901 A044860 * A088449 A104010 A102544
Adjacent sequences: A161421 A161422 A161423 * A161425 A161426 A161427
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KEYWORD
| easy,nonn
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AUTHOR
| Omar E. Pol (info(AT)polprimos.com), Jun 20 2009
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EXTENSIONS
| Terms beyond a(8) 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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