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Search: id:A112017
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| A112017 |
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Composite solutions of the form 4k+3 of the equation (*): sigma(phi(sigma(x)))=phi(sigma(phi(x)). |
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+0
2
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| 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
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OFFSET
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1,1
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COMMENT
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114190259 is the smallest prime solution of the form 4k+3 of the equation (*). Sequence A112016 gives such solutions.
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MATHEMATICA
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Do[If[ !PrimeQ[m]&& Mod[m, 4]==3&&DivisorSigma[1, EulerPhi[ DivisorSigma[1, m]]]==EulerPhi[DivisorSigma[1, EulerPhi[m]]], Print[m]], {m, 5600000}]
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CROSSREFS
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Cf. A112016.
Sequence in context: A133539 A100970 A159202 this_sequence A031935 A137873 A054814
Adjacent sequences: A112014 A112015 A112016 this_sequence A112018 A112019 A112020
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KEYWORD
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easy,nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Sep 15 2005
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