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A283246
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Numbers k such that (17*10^k - 179)/9 is prime.
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0
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4, 5, 10, 13, 16, 106, 130, 148, 880, 1261, 2560, 2629, 3730, 5284, 7411, 8255, 9091, 9490, 10171, 14033, 25618, 39382, 47452
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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 1 followed by k-2 occurrences of the digit 8 followed by the digits 69 is prime (see Example section).
a(24) > 2*10^5.
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LINKS
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EXAMPLE
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5 is in this sequence because (17*10^5 - 179)/9 = 188869 is prime.
Initial terms and primes associated:
a(1) = 4, 18869;
a(2) = 5, 188869;
a(3) = 10, 18888888869;
a(4) = 13, 18888888888869;
a(5) = 16, 18888888888888869; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[(17*10^# - 179)/9] &]
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PROG
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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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STATUS
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approved
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