Search: id:A066950
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%I A066950
%S A066950 1,11,18,75,172,372,482,732,3276,7965,13068,46476,103488,252240,727956,
%T A066950 1795605,6030528,8769600,15436092,56747712,224518995,297780084,
%U A066950 317961000,855489144,2691137721
%N A066950 Numbers n such that phi(sigma(n)) + sigma(phi(n)) = 2n.
%C A066950 a(26) > 3*10^9. [From Donovan Johnson (donovan.johnson(AT)yahoo.com), 
               Sep 16 2009]
%e A066950 phi(sigma(11)) + sigma(phi(11)) = phi(12) + sigma(10) = 4 + 18 = 2*11, 
               so 11 is in the sequence.
%t A066950 f[n_] := EulerPhi[DivisorSigma[1, n]]+DivisorSigma[1, EulerPhi[n]]; Select[Range[1, 
               10^5], f[ # ]==2*#&]
%Y A066950 Cf. A000010, A000203.
%Y A066950 Sequence in context: A151748 A003334 A037006 this_sequence A162011 A123248 
               A111477
%Y A066950 Adjacent sequences: A066947 A066948 A066949 this_sequence A066951 A066952 
               A066953
%K A066950 more,nonn
%O A066950 1,2
%A A066950 Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 25 2002
%E A066950 Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jan 26 2002
%E A066950 a(20)-a(25) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 
               16 2009

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