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

1843, 2231, 12707, 20003, 58091, 72971, 129899, 153851, 876987, 899991, 909131, 1154535, 1660931, 1835503, 2003303, 2184463, 2200979, 2248307, 2482667, 2518571, 2566463, 2699723, 2978371, 2982815, 3537163, 4814207, 4831439

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..27.

Mathematica

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

Crossrefs

Cf. A112016.

Sequence in context: A287172 A243482 A252214 * A297894 A290393 A251109

Adjacent sequences: A112014 A112015 A112016 * A112018 A112019 A112020

Keyword

easy,nonn

Author

Farideh Firoozbakht, Sep 15 2005

Status

approved