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A296094
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Numbers k such that (43*10^k + 47)/9 is prime.
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0
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1, 3, 7, 12, 15, 21, 85, 177, 204, 477, 487, 1686, 2179, 2815, 2892, 3466, 7308, 17883, 25431, 69048, 89169, 126441
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 7 followed by the digits 83 is prime (see Example section).
a(23) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (43*10^3 + 47)/9 = 4783 is prime.
Initial terms and primes associated:
a(1) = 1, 53;
a(2) = 3, 4783;
a(3) = 7, 47777783;
a(4) = 12, 4777777777783;
a(5) = 15, 4777777777777783; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(43*10^# + 47)/9] &]
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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