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A056654
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Numbers k such that 10*R_k + 3 is prime, where R_k is the repunit (A002275) of length k.
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507
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0, 1, 2, 4, 8, 10, 23, 83, 220, 1313, 2951, 20015, 51053
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OFFSET
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1,3
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COMMENTS
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Also numbers k such that (10^(k+1)+17)/9 is prime.
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LINKS
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FORMULA
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EXAMPLE
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8 is a term because 111111113 is a prime.
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MATHEMATICA
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Do[ m = n; If[ primeQ[ 10*(10^n - 1)/9 + 3 ], Print[ n ] ], {n, 1, 1350} ]
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PROG
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CROSSREFS
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KEYWORD
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hard,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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