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A293593
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Numbers k such that (26*10^k - 413)/9 is prime.
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0
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3, 4, 6, 12, 15, 19, 36, 40, 484, 576, 2328, 2841, 4008, 4878, 5190, 10149, 10383, 11982, 21082, 46324, 61156, 83638, 125886
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OFFSET
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1,1
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COMMENTS
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For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 8 followed by the digits 43 is prime (see Example section).
a(24) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (26*10^3 - 413)/9 = 2843 is prime.
Initial terms and primes associated:
a(1) = 3, 2843;
a(2) = 4, 28843;
a(3) = 6, 2888843;
a(4) = 12, 2888888888843;
a(5) = 15, 2888888888888843; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[(26*10^# - 413)/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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