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A278397
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Numbers k such that 10^k - 20001 is prime.
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1
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5, 11, 16, 21, 37, 83, 94, 299, 318, 467, 622, 707, 1931, 2175, 2189, 2238, 2526, 5202, 10541, 15822, 17407, 19919, 19998, 25407, 96377, 118009
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OFFSET
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1,1
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COMMENTS
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For k > 4, numbers k such that k-5 occurrences of the digit 9 followed by the digits 79999 is prime (see Example section).
a(27) > 2*10^5.
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LINKS
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EXAMPLE
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5 is in this sequence because 10^5 - 20001 = 79999 is prime.
Initial terms and associated primes:
a(1) = 5, 79999;
a(2) = 11, 99999979999;
a(3) = 16, 9999999999979999;
a(4) = 21, 999999999999999979999;
a(5) = 37, 9999999999999999999999999999999979999; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[10^# - 20001] &]
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PROG
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(Magma) [n: n in [5..400] | IsPrime(10^n - 20001)]; // Vincenzo Librandi, Nov 21 2016
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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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