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A099421
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0 together with numbers k such that 8*R_k - 7 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.
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2
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0, 3, 19, 79, 139, 223, 463, 544, 1096, 1419, 3247, 3877, 4417, 9507, 11091, 14602, 27811, 29188
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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 abs(8*10^k - 71)/9 is a prime.
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LINKS
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FORMULA
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MATHEMATICA
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Do[ If[ PrimeQ[ 8(10^n - 1)/9 - 7], Print[n]], {n, 0, 15000}]
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PROG
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(PARI)
for(n=0, 10^4, if(ispseudoprime(abs(8*(10^n-1)/9-7)), print1(n, ", "))) \\ Derek Orr, Sep 06 2014
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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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STATUS
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approved
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