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Search: id:A140349
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| A140349 |
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A number n is included if both (the largest divisor of n that is <= sqrt(n)) and ((the smallest divisor of n that is >= sqrt(n)) are composite. |
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1
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| 16, 24, 32, 36, 48, 54, 60, 64, 72, 80, 81, 90, 96, 100, 108, 112, 120, 126, 128, 135, 140, 144, 150, 160, 162, 168, 180, 189, 192, 196, 200, 210, 216, 224, 225, 240, 243, 250, 252, 256, 264, 270, 280, 288, 294, 300, 308, 315, 320, 324, 330, 336, 350, 352, 360
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OFFSET
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1,1
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COMMENT
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All numbers that are each the square of a composite are included in the sequence. All numbers that are the square of a prime are excluded from the sequence.
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EXAMPLE
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The divisors of 80 are 1,2,4,5,8,10,16,20,40,80. The middle two divisors are 8 and 10, which are both composite. So 80 is included in the sequence.
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MATHEMATICA
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fQ[n_] := Block[{m = DivisorSigma[0, n]}, Union@ PrimeQ@ Take[ Divisors@ n, {Floor[(m + 1)/2], Ceiling[(m + 1)/2]}] == {False}]; Select[ Range[2, 363], fQ@# &] - Robert G. Wilson v, (rgwv(AT)rgwv.com), May 31 2008
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CROSSREFS
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Sequence in context: A105732 A114415 A033987 this_sequence A088493 A074451 A082803
Adjacent sequences: A140346 A140347 A140348 this_sequence A140350 A140351 A140352
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), May 29 2008
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EXTENSIONS
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More terms from Robert G. Wilson v, (rgwv(AT)rgwv.com), May 31 2008
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