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A183181
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Numbers k such that (7*10^(2*k+1) - 9*10^k - 7)/9 is prime.
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2
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4, 5, 8, 11, 1244, 1685, 2009, 14657, 15118, 20332, 50830, 75062
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OFFSET
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1,1
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REFERENCES
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C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
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LINKS
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FORMULA
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MATHEMATICA
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Do[If[PrimeQ[(7*10^(2n + 1) - 9*10^n - 7)/9], Print[n]], {n, 3000}]
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PROG
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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