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A278960
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Numbers k such that 4*10^k - 99 is prime.
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0
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4, 6, 7, 9, 43, 53, 67, 69, 123, 178, 201, 448, 649, 658, 1068, 2003, 2584, 4445, 4816, 6322, 8477, 8868, 14500, 24934, 33412, 42504, 87287, 87337
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OFFSET
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1,1
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COMMENTS
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For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 9 followed by the digits 01 is prime (see Example section).
a(29) > 2*10^5.
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LINKS
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EXAMPLE
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4 is in this sequence because 4*10^4 - 99 = 39901 is prime.
Initial terms and associated primes:
a(1) = 4, 39901;
a(2) = 6, 3999901;
a(3) = 7, 39999901;
a(4) = 9, 3999999901;
a(5) = 43, 39999999999999999999999999999999999999999901; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[4*10^# - 99] &]
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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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EXTENSIONS
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Link and Mathematica program corrected by Robert Price, Jun 11 2018
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STATUS
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approved
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