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A248888
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Numbers k such that prime(k) <= 2*sigma(k).
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0
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1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 24, 28, 30, 36, 40, 42, 48, 60, 72, 84, 90, 96, 120, 180
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OFFSET
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1,2
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COMMENTS
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Obviously only for n = 1, prime(n) = 2*sigma(n).
It is interesting that all terms of the sequence A112587 are in the sequence and this sequence has only two more terms 96 & 180. Hence if phi(n) <= 2*tau(n) then prime(n) <= 2*sigma(n).
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LINKS
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MATHEMATICA
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Select[Range[200], Prime[#] <= 2DivisorSigma[1, #]&]
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CROSSREFS
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KEYWORD
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nonn,fini,full
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AUTHOR
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STATUS
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approved
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