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A161345
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Numbers k whose largest divisor <= sqrt(k) is 3.
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39
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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
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OFFSET
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1,1
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COMMENTS
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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. - R. J. Mathar, Jun 24 2009
See also the array in A163280, the main entry for this sequence. - Omar E. Pol, Oct 24 2009
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LINKS
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FORMULA
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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; # R. J. Mathar, Jun 24 2009
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MATHEMATICA
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md3Q[n_]:=Max[Select[Divisors[n], #<=Sqrt[n]&]]==3; Select[Range[800], md3Q] (* Harvey P. Dale, Aug 12 2013 *)
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CROSSREFS
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Cf. A000005, A018253, A160811, A160812, A161205, A161344, A161346, A033676, A008578, A161424, A161835, A162526, A162527, A162528, A162529, A162530, A162531, A162532.
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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