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Search: id:A123047
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| A123047 |
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Numbers n such that n divides 5^n + 4. |
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2
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OFFSET
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1,2
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COMMENT
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Numbers n up to 10^6 such that n divides 5^n - 4 are {1,4769}.
n must be odd since any power of 5 plus 4 is odd. - Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 14 2006
There is no further term up to 10^9. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Nov 18 2006
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MATHEMATICA
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Do[ If[ PowerMod[5, 2n - 1, 2n - 1] + 5 == 2n, Print[2n - 1]], {n, 10^9}] (* Robert G. Wilson v *)
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CROSSREFS
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Cf. A067946: n | 5^n-1; A015951: n | 5^n+1.
Adjacent sequences: A123044 A123045 A123046 this_sequence A123048 A123049 A123050
Sequence in context: A041867 A134711 A108713 this_sequence A097420 A037119 A113558
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KEYWORD
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hard,more,nonn
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AUTHOR
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Alexander Adamchuk (alex(AT)kolmogorov.com), Nov 04 2006
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EXTENSIONS
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a(4) & a(5) from Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 14 2006
One more term from Ryan Propper (rpropper(AT)stanford.edu), Mar 23 2007
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