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A295625
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Numbers k such that (388*10^k - 1)/9 is prime.
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0
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0, 1, 7, 12, 16, 18, 37, 67, 82, 90, 133, 622, 624, 1464, 1963, 4741, 4824, 13861, 18423, 61374
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OFFSET
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1,3
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COMMENTS
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For k > 1, numbers such that the digits 43 followed by k occurrences of the digit 1 is prime (see Example section).
a(21) > 2*10^5.
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LINKS
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EXAMPLE
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1 is in this sequence because (388*10^1 - 1)/9 = 431 is prime.
Initial terms and primes associated:
a(1) = 0, 43;
a(2) = 1, 431;
a(3) = 7, 431111111;
a(4) = 12, 43111111111111;
a(5) = 16, 431111111111111111; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(388*10^# - 1)/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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STATUS
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approved
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