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A074874 Numbers n such that phi(n + phi(n)) = sigma(n). 2

%I #7 Feb 11 2014 19:05:30

%S 1,3,5,11,23,55,87,123,383,501,957,1015,3565,3777,5667,6141,9069,

%T 11033,13827,27347,35119,44693,55645,91915,137037,156919,180251,

%U 233935,261989,269395,294679,315605,335995,361645,380103,389809,410201,428399,443267

%N Numbers n such that phi(n + phi(n)) = sigma(n).

%H Donovan Johnson, <a href="/A074874/b074874.txt">Table of n, a(n) for n = 1..500</a>

%e sigma(23) = 24 = phi(23 + 22) = phi(23 + phi(23)), so 23 is a term of the sequence.

%e phi(87 + phi(87)) = phi(87 + 56) = 120 = sigma(87), so 87 is a member of the sequence.

%t Select[Range[10^5], EulerPhi[ # + EulerPhi[ # ]] == DivisorSigma[1, # ] &]

%K nonn

%O 1,2

%A _Joseph L. Pe_, Sep 12 2002

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Last modified March 28 04:13 EDT 2024. Contains 371235 sequences. (Running on oeis4.)