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A259138
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Numbers k such that R_k + 7*10^k + 6 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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1,2
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COMMENTS
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Also, numbers k such that (64*10^k + 53)/9 is prime.
Terms from Kamada data.
Note that Kamada does not recognize k=0 as 13 is a degenerate case of form ABB..BBA.
a(4) > 1.2*10^6.
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LINKS
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EXAMPLE
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For k=10906, R_k + 7*10^k + 6 = R_10906 + 7*10^10906 + 6 = 711...117 which is prime.
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MATHEMATICA
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Select[Range[0, 1200000], PrimeQ[(64*10^#+53)/9] &]
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CROSSREFS
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KEYWORD
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nonn,bref,more,hard
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AUTHOR
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STATUS
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approved
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