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A074876 Numbers n such that sigma(sigma(n) - phi(n)) = phi(sigma(n) + phi(n)). 0

%I

%S 4,16,85,923,6713,8035,8827,10109,19349,21671,30565,31499,41285,

%T 116129,154255,269009,282799,312997,362483,477325,486301,498329,

%U 525083,607057,609367,714589,995087,1038841,2013187,2084785,2088545,2148409,2185937

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

%e sigma(sigma(85) - phi(85)) = sigma(108 - 64) = 84; phi(sigma(85) + phi(85)) = phi(108 + 64) = 84, so 85 is a term of the sequence.

%t r = {}; Do[d = DivisorSigma[1, n]; e = EulerPhi[n]; If[DivisorSigma[1, d - e] == EulerPhi[d + e], r = Append[r, n]], {n, 1, 10^5}]; r

%K nonn

%O 1,1

%A _Joseph L. Pe_, Sep 12 2002

%E a(14)-a(33) from _Donovan Johnson_, Feb 17 2010

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Last modified October 1 08:04 EDT 2022. Contains 357135 sequences. (Running on oeis4.)