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A099006
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Numbers k such that 2*10^k + 5*R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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1
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2, 3, 26, 27, 45, 62, 147, 1277, 1665, 1979, 2970, 12773, 17702, 19128, 22206, 22386, 25053
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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 (23*10^k + 13)/9 is prime.
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LINKS
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FORMULA
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EXAMPLE
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n = 2, 3, 26, 27 are members since 257, 2557, 255555555555555555555555557 and
2555555555555555555555555557 are primes.
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MATHEMATICA
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Do[ If[ PrimeQ[(23*10^n + 13)/9], Print[n]], {n, 0, 10000}]
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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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Julien Peter Benney (jpbenney(AT)ftml.net), Nov 07 2004
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EXTENSIONS
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a(8), a(9), a(10) & a(11) from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 17 2004
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STATUS
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approved
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