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A112018 Primes p of the form 4k+3 where sigma(phi(sigma(p)))= phi(sigma(phi(p))). 0
114190259, 6364631939, 10296994891, 10429820759 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Between the first 480000000 primes, the equation (*): sigma(phi(sigma(x)))=phi(sigma(phi(x))) has 256 solutions q(i) and only four of them namely q(76),q(215),q(254) and q(256) are of the form 4k+3. Sequence A112017 gives composite solutions of the equation (*), which are of the form 4k+3.

LINKS

Table of n, a(n) for n=1..4.

MATHEMATICA

Do[If[Mod[Prime[m], 4]==3 && DivisorSigma[1, EulerPhi[Prime[m]+1 ==EulerPhi[DivisorSigma[1, Prime[m]-1]], Print[Prime[m]]], {m, 480000000}]

CROSSREFS

Cf. A112017.

Sequence in context: A171571 A208491 A205169 * A216010 A206751 A206062

Adjacent sequences:  A112015 A112016 A112017 * A112019 A112020 A112021

KEYWORD

more,nonn

AUTHOR

Farideh Firoozbakht, Sep 15 2005

STATUS

approved

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Last modified April 8 08:04 EDT 2020. Contains 333313 sequences. (Running on oeis4.)