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A259129
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Numbers k such that 2*R_k + 3*10^k + 1 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
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0
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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 (29*10^k + 7)/9 is prime.
Terms from Kamada data.
a(7) > 10^5.
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LINKS
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EXAMPLE
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For k=6, 2*R_6 + 3*10^k + 1 = 222222 + 3000000 + 1 = 3222223 which is prime.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(29*10^#+7)/9] &]
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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STATUS
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approved
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