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A206447
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Composite numbers n such that sigma(n) = sigma(d) has solution for some other composite number d.
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1
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14, 15, 16, 20, 24, 25, 26, 28, 30, 33, 35, 38, 39, 40, 42, 44, 46, 48, 51, 54, 55, 56, 58, 60, 62, 65, 66, 68, 69, 70, 75, 77, 78, 80, 82, 84, 87, 88, 90, 92, 94, 95, 96, 99, 102, 104, 105, 108, 110, 112, 114, 115, 116, 118, 119, 120, 122, 123, 124, 125
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..60.
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EXAMPLE
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Composite numbers 14 and 15 are in sequence because sigma(14) = sigma(15) = 24.
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MATHEMATICA
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t2 = Table[If[PrimeQ[n], 0, DivisorSigma[1, n]], {n, 1000}]; Select[Range[132], ! PrimeQ[#] && Length[Position[t2, t2[[#]]]] > 1 &] (* T. D. Noe, Feb 27 2012 *)
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CROSSREFS
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Cf. A206036, A158913, A066073.
Sequence in context: A089838 A048125 A163482 * A130687 A173687 A220671
Adjacent sequences: A206444 A206445 A206446 * A206448 A206449 A206450
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KEYWORD
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nonn
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AUTHOR
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Jaroslav Krizek, Feb 07 2012
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STATUS
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approved
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