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 A161345 Numbers k whose largest divisor <= sqrt(k) is 3. 37
 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; refs; listen; history; text; internal format)
 OFFSET 1,1 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=3 and cannot be eliminated by any sieve s >= 4. - R. J. Mathar, Jun 24 2009 See A161344 for more information. - Omar E. Pol, Jul 05 2009 See also the array in A163280, the main entry for this sequence. - Omar E. Pol, Oct 24 2009 LINKS Omar E. Pol, Illustration: Divisors and pi(x) Omar E. Pol, Illustration for A008578, A161344, A161345 and A161424 [From Omar E. Pol, Oct 24 2009] FORMULA Numbers k such that A033676(k)=3. - Omar E. Pol, Jul 05 2009 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: 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 MATHEMATICA md3Q[n_]:=Max[Select[Divisors[n], #<=Sqrt[n]&]]==3; Select[Range[800], md3Q] (* Harvey P. Dale, Aug 12 2013 *) CROSSREFS Cf. A000005, A018253, A160811, A160812, A161205, A161344, A161346, A033676, A008578, A161424, A161835, A162526, A162527, A162528, A162529, A162530, A162531, A162532. Cf. Third column of the array in A163280. Also, third row of array in A163990. - Omar E. Pol, Oct 24 2009 Sequence in context: A138945 A119486 A235341 * A102655 A308748 A120167 Adjacent sequences:  A161342 A161343 A161344 * A161346 A161347 A161348 KEYWORD easy,nonn AUTHOR Omar E. Pol, Jun 20 2009 EXTENSIONS Terms beyond a(10) from R. J. Mathar, Jun 24 2009 Definition added by R. J. Mathar, Jun 28 2009 STATUS approved

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Last modified January 23 13:40 EST 2020. Contains 331171 sequences. (Running on oeis4.)