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 A066950 Numbers n such that phi(sigma(n)) + sigma(phi(n)) = 2n. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(26) > 3*10^10. - Donovan Johnson, Mar 05 2014 LINKS EXAMPLE phi(sigma(11)) + sigma(phi(11)) = phi(12) + sigma(10) = 4 + 18 = 2*11, so 11 is in the sequence. MATHEMATICA f[n_] := EulerPhi[DivisorSigma[1, n]]+DivisorSigma[1, EulerPhi[n]]; Select[Range[1, 10^5], f[ # ]==2*#&] CROSSREFS Cf. A000010, A000203. Sequence in context: A168433 A302455 A303237 * A214495 A162011 A123248 Adjacent sequences:  A066947 A066948 A066949 * A066951 A066952 A066953 KEYWORD more,nonn AUTHOR Joseph L. Pe, Jan 25 2002 EXTENSIONS Edited by Dean Hickerson, Jan 26 2002 a(20)-a(25) from Donovan Johnson, Sep 16 2009 STATUS approved

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Last modified June 14 10:04 EDT 2021. Contains 345025 sequences. (Running on oeis4.)