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A103066
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Numbers n such that 7*10^n + 8*R_n - 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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1
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0, 1, 3, 6, 60, 288, 1314, 1728, 2493, 13893, 13944, 17100, 70227
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OFFSET
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1,3
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COMMENTS
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Also numbers n such that (71*10^n-53)/9 is prime.
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LINKS
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FORMULA
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EXAMPLE
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For n=0, (71*10^n-53)/9 = 2 which is prime.
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MATHEMATICA
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Do[ If[ PrimeQ[(71*10^n - 53)/9], Print[n]], {n, 0, 10000}]
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PROG
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(PARI) for(n=0, 10^5, if(isprime((71*10^n-53)/9), print1(n", "))); \\ Altug Alkan, Oct 06 2015
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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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EXTENSIONS
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Inserted a(1)=0 and added a(13) by Robert Price, Oct 06 2015
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STATUS
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approved
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