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A097683
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Numbers k such that R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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7
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0, 1, 2, 3, 5, 9, 11, 24, 84, 221, 1314, 2952, 20016, 51054
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OFFSET
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1,3
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COMMENTS
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Also numbers k such that (10^k + 17)/9 is prime.
The corresponding values R_k + 2 are primes of the form "(n-1) ones followed by a three"; zero is a degenerate case. Related to the base-10 repunit primes.
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LINKS
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FORMULA
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EXAMPLE
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11113 = ((10^5)+17)/9 and 11113 is prime.
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MAPLE
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MATHEMATICA
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Do[ If[ PrimeQ[(10^n - 1)/9 + 2], Print[n]], {n, 0, 5951}] (* Robert G. Wilson v, Oct 15 2004 *)
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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Carl R. White and Julien Peter Benney (jpbenney(AT)ftml.net), Aug 19 2004
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EXTENSIONS
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STATUS
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approved
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