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A097685
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Numbers k such that R_k + 8 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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3
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2, 5, 6, 8, 17, 50, 684, 720, 1452, 1679, 3146, 72821, 111902, 146063, 180689, 330906
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OFFSET
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1,1
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COMMENTS
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Also numbers k such that (10^k + 71)/9 is prime.
The corresponding values R_k + 8 are primes of the form "(k-1) ones followed by a nine". Related to the base-10 repunit primes.
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LINKS
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FORMULA
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MATHEMATICA
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Do[ If[ PrimeQ[(10^n - 1)/9 + 8], Print[n]], {n, 0, 5000}] (* Robert G. Wilson v, Oct 14 2004 *)
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CROSSREFS
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KEYWORD
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nonn,more,hard,changed
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AUTHOR
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EXTENSIONS
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a(13)-a(16) from Kamada data by Tyler Busby, May 03 2024
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STATUS
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approved
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