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A048969
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Composite numbers k such that sigma(k) / d(k) is prime.
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4
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6, 20, 45, 49, 150, 169, 361, 832, 961, 1445, 1734, 1849, 5329, 8405, 9409, 9477, 10086, 10609, 14580, 14641, 16129, 17405, 20886, 24649, 25205, 30246, 39601, 39605, 47526, 49729, 51005, 58081, 61206, 73441, 85805, 102966, 139445, 149645, 167281, 167334
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OFFSET
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1,1
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LINKS
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EXAMPLE
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For k=6 (composite), sigma(6)=12, d(6)=4 and 12/4 = 3 is prime.
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MATHEMATICA
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nn=62000; With[{comps=Complement[Range[nn], Prime[Range[PrimePi[nn]]]]}, Select[ comps, PrimeQ[DivisorSigma[1, #]/DivisorSigma[0, #]]&]] (* Harvey P. Dale, Feb 19 2012 *)
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CROSSREFS
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KEYWORD
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nice,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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