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A056718
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Numbers k such that (61*10^k - 7)/9 is prime.
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1
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1, 2, 4, 10, 13, 25, 115, 179, 181, 238, 785, 799, 1193, 1730, 1811, 1871, 2116, 2180, 17878, 22093, 30976, 31631, 43271, 52763, 66575
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OFFSET
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1,2
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COMMENTS
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Or, numbers k such that 6*10^k + 7*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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LINKS
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MATHEMATICA
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Do[ If[ PrimeQ[ 6*10^n + 7*(10^n-1)/9], Print[n]], {n, 0, 5000}]
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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The PRP's corresponding to 2116 and 2180 have been proved to be prime by Maksym Voznyy (mvoznyy0526(AT)rogers.com), Jan 05 2008, who has found 2 new PRP's, which correspond to 17878 and 22093
30976, 31631 and 43271 from Maksym Voznyy, Jan 2008 confirmed as next terms of sequence by Ray Chandler, Feb 06 2012
52763 from Serge Batalov, Feb 27 2009 confirmed as next term of sequence by Ray Chandler, Feb 06 2012
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STATUS
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approved
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