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Search: id:A070806
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| A070806 |
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Cototient(totient(n))=A070556(n) is a power of 2 and n is a prime number. |
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+0
5
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| 3, 5, 7, 13, 17, 29, 97, 113, 193, 257, 449, 509, 769, 7937, 12289, 65537, 114689, 520193, 786433
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OFFSET
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1,1
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EXAMPLE
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Powers of 2 observable in A070556[this sequence]= {1,2,4,8,16,64,128,256,512,4096,8192,32768,65536,262144,524288,..}. For F(m),Fermat prime:phi[F(m)]=2^m, cototient[2^m]=2^(m-1); If n=113: phi[113]=112,cototient[112]=112-48=64, so 113 is here.
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MATHEMATICA
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Do[s= EulerPhi[n]-EulerPhi[EulerPhi[n]]; If[IntegerQ[Log[2, s]]&&PrimeQ[n], Print[n]], {n, 1, 10000000}]
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CROSSREFS
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Cf. A070556, A051953, A054571, A070807, A070809-A070811.
Sequence in context: A137270 A071111 A038929 this_sequence A003424 A073638 A066464
Adjacent sequences: A070803 A070804 A070805 this_sequence A070807 A070808 A070809
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KEYWORD
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more,nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), May 08 2002
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