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A112017 Composite solutions of the form 4k+3 of the equation (*): sigma(phi(sigma(x)))=phi(sigma(phi(x)). 1

%I

%S 1843,2231,12707,20003,58091,72971,129899,153851,876987,899991,909131,

%T 1154535,1660931,1835503,2003303,2184463,2200979,2248307,2482667,

%U 2518571,2566463,2699723,2978371,2982815,3537163,4814207,4831439

%N Composite solutions of the form 4k+3 of the equation (*): sigma(phi(sigma(x)))=phi(sigma(phi(x)).

%C 114190259 is the smallest prime solution of the form 4k+3 of the equation (*). Sequence A112016 gives such solutions.

%t Do[If[ !PrimeQ[m]&& Mod[m, 4]==3&&DivisorSigma[1, EulerPhi[ DivisorSigma[1, m]]]==EulerPhi[DivisorSigma[1, EulerPhi[m]]], Print[m]], {m, 5600000}]

%Y Cf. A112016.

%K easy,nonn

%O 1,1

%A _Farideh Firoozbakht_, Sep 15 2005

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Last modified January 19 16:49 EST 2022. Contains 350466 sequences. (Running on oeis4.)