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A281142
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Numbers k such that (25*10^k - 13)/3 is prime.
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0
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1, 2, 3, 6, 8, 18, 21, 33, 56, 301, 381, 426, 769, 1123, 1638, 2037, 2660, 3284, 4723, 5686, 17227, 22084, 25009, 36176, 125076, 141019
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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 8 followed by k-2 occurrences of the digit 3 followed by the digits 29 is prime (see Example section).
a(27) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (25*10^3 - 13) / 3 = 8329 is prime.
Initial terms and primes associated:
a(1) = 1, 79;
a(2) = 2, 829;
a(3) = 3, 8329;
a(4) = 6, 8333329;
a(5) = 8, 833333329; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(25*10^# - 13) / 3] &]
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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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