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%I #15 Feb 24 2019 01:57:16
%S 16,20,24,28,32,44,52,68,76,92,116,124,148,164,172,188,212,236,244,
%T 268,284,292,316,332,356,388,404,412,428,436,452,508,524,548,556,596,
%U 604,628,652,668,692,716,724,764,772,788,796,844,892,908,916,932,956,964
%N Numbers k whose largest divisor <= sqrt(k) equals 4.
%C 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. - _R. J. Mathar_, Jun 24 2009
%C See A161344 for more information. - _Omar E. Pol_, Jul 05 2009
%C See also the array in A163280, the main entry for this sequence. - _Omar E. Pol_, Oct 24 2009
%H Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>
%H Omar E. Pol, <a href="http://www.polprimos.com/imagenespub/polprdipi.jpg">Illustration: Divisors and pi(x)</a>
%H Omar E. Pol, <a href="http://www.polprimos.com/imagenespub/poldiv06.jpg">Illustration for A008578, A161344, A161345 and A161424</a> [From _Omar E. Pol_, Oct 24 2009]
%F Numbers n such that A033676(n)=4. - _Omar E. Pol_, Jul 05 2009
%p 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; # _R. J. Mathar_, Jun 24 2009
%t Select[Range[1, 1000], Function[m, Max[Select[Divisors[m], # <= Sqrt[m] &]] == 4]] (* _Ashton Baker_, Nov 03 2013 *)
%Y Cf. A000005, A018253, A160811, A160812, A161205, A161344, A161345, A161346, A161425, A161428, A033676, A008578, A161835, A162526, A162527, A162528, A162529, A162530, A162531, A162532.
%Y Cf. Fourth column of array in A163280. Also, fourth row of array in A163990. - _Omar E. Pol_, Oct 24 2009
%K easy,nonn
%O 1,1
%A _Omar E. Pol_, Jun 20 2009
%E Terms beyond a(8) from _R. J. Mathar_, Jun 24 2009
%E Definition added by _R. J. Mathar_, Jun 28 2009
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