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A183179
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Numbers n such that 7*(10^(2n+1)-1)/9 - 3*10^n is prime.
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2
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2, 3, 6, 23, 36, 69, 561, 723, 3438, 4104, 9020, 13977, 19655, 32400
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OFFSET
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1,1
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COMMENTS
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Original name: Numbers n such that (7*10^(2n+1)-27*10^n-7)/9 is prime.
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REFERENCES
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C. Caldwell and H. Dubner, The near repdigit primes A(n-k-1)B(1)A(k), especially 9(n-k-1)8(1)9(k), 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) - 27*10^n - 7)/9], Print[n]], {n, 3000}]
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PROG
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(PARI) for(n=1, 1e3, if(ispseudoprime((7*10^(2*n+1)-27*10^n-7)/9), print1(n, ", "))) \\ Altug Alkan, Nov 23 2015
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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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