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Search: id:A074777
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| A074777 |
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Integers n such that sigma(phi(n))/n = 1/2. |
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+0
1
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OFFSET
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1,1
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COMMENT
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Since 2^2^n+1 is prime for n=0,1,...,4 (Fermat primes), 2^(2^(n-1)+1)-2 is in the sequence for n=1,2,...,6. Conjecture: There are no further terms. - Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Sep 14 2004
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FORMULA
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For n=1, 2, ..., 6, a(n)=2^(2^(n-1)+1)-2. - Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Sep 14 2004
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CROSSREFS
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Cf. A062402.
Sequence in context: A076926 A092023 A112723 this_sequence A007280 A102927 A127295
Adjacent sequences: A074774 A074775 A074776 this_sequence A074778 A074779 A074780
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KEYWORD
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nonn
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AUTHOR
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Antonio G. Astudillo (afg_astudillo(AT)hotmail.com), Sep 07 2002
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EXTENSIONS
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8589934590 from Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Sep 14 2004
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