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A066228
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The EulerPhi(sigma(EulerPhi))-perfect numbers, where the f-perfect numbers for an arithmetical function f are defined in A066218.
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0
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OFFSET
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1,1
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COMMENTS
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There are no terms between 449 and 10^5. Are there any more terms? Are there infinitely many?
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LINKS
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EXAMPLE
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Let f(n) = EulerPhi(sigma(EulerPhi(n)). Proper divisors of 28 = {1, 2, 4, 7, 14}; the sum of their f-values = 1+1+2+4+4 = 12 = f(28); hence 28 belongs to the sequence.
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MATHEMATICA
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f[x_] := EulerPhi[DivisorSigma[1, EulerPhi[x]]]; Select[ Range[ 1, 10^5], 2 * f[ # ] == Apply[ Plus, Map[ f, Divisors[ # ] ] ] & ]
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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