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A289811
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Numbers k such that (13*10^k + 401)/9 is prime.
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0
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1, 3, 4, 6, 7, 15, 18, 57, 75, 82, 358, 1347, 2278, 2577, 4156, 6712, 7471, 14437, 15247, 28251, 62914, 78213, 158694
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 4 followed by the digits 89 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 (13*10^3 + 401)/9 = 1489 is prime.
Initial terms and associated primes:
a(1) = 1, 59;
a(2) = 3, 1489;
a(3) = 4, 14489;
a(4) = 6, 1444489;
a(5) = 7, 14444489; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(13*10^# + 401)/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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