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Search: id:A112018
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| A112018 |
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Primes p of the form 4k+3 where sigma(phi(sigma(p)))= phi(sigma(phi(p))). |
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OFFSET
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1,1
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COMMENT
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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.
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MATHEMATICA
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Do[If[Mod[Prime[m], 4]==3 && DivisorSigma[1, EulerPhi[Prime[m]+1 ==EulerPhi[DivisorSigma[1, Prime[m]-1]], Print[Prime[m]]], {m, 480000000}]
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CROSSREFS
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Cf. A112017.
Sequence in context: A038451 A068538 A147581 this_sequence A157770 A015380 A038131
Adjacent sequences: A112015 A112016 A112017 this_sequence A112019 A112020 A112021
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KEYWORD
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more,nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Sep 15 2005
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