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Search: id:A097652
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| A097652 |
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Numbers n such that n=phi(phi(n)+sigma(n)) and n is not of the form 2*p where p is a Sophie Germain odd prime. |
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2
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| 1, 2, 20, 48, 180, 208, 864, 1120, 1368, 3552, 58320, 76416, 79968, 95488, 107520, 338688, 570240, 595968, 653184, 1347840, 5199552, 7918848, 14592000
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OFFSET
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1,2
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COMMENT
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It is obvious that if n=2*p where p is a Sophie Germain odd prime then n=phi(phi(n)+sigma(n)). This sequence is a subsequence of A097646. Except for the first term all terms of this sequence are even. There is no other term up t0 3*10^7.
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LINKS
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C. K. Caldwell, The Prime Glossary, Sophie Germain prime.
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EXAMPLE
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14592000 is in the sequence because 14592000=2*7296000, 7296000 is not a Sophie Germain odd prime and phi(phi(14592000)+sigma(14592000)) =14592000.
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MATHEMATICA
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Do[If[(!PrimeQ[n/2]||!PrimeQ[n+1])&&n==EulerPhi[EulerPhi[n]+ DivisorSigma[1, n]], Print[n]], {n, 30000000}]
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CROSSREFS
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Cf. A097646, A005384.
Sequence in context: A062133 A050684 A073214 this_sequence A059211 A139271 A133217
Adjacent sequences: A097649 A097650 A097651 this_sequence A097653 A097654 A097655
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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 09 2004
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