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A066950
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Numbers k such that phi(sigma(k)) + sigma(phi(k)) = 2k.
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1
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1, 11, 18, 75, 172, 372, 482, 732, 3276, 7965, 13068, 46476, 103488, 252240, 727956, 1795605, 6030528, 8769600, 15436092, 56747712, 224518995, 297780084, 317961000, 855489144, 2691137721, 58016937600, 127198874880, 228517311456, 411814778112
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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phi(sigma(11)) + sigma(phi(11)) = phi(12) + sigma(10) = 4 + 18 = 2*11, so 11 is in the sequence.
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MATHEMATICA
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f[n_] := EulerPhi[DivisorSigma[1, n]]+DivisorSigma[1, EulerPhi[n]]; Select[Range[1, 10^5], f[ # ]==2*#&]
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CROSSREFS
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KEYWORD
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more,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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