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A294126
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Numbers k such that (44*10^k - 791)/9 is prime.
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0
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2, 3, 9, 15, 20, 23, 63, 66, 75, 93, 120, 480, 504, 812, 872, 1124, 3888, 9882, 14859, 33786, 44736, 83768
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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 4 followed by k-2 occurrences of the digit 8 followed by the digits 01 is prime (see Example section).
a(23) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (44*10^2 - 791)/9 = 401 is prime.
Initial terms and associated primes:
a(1) = 2, 401;
a(2) = 3, 4801;
a(3) = 9, 4888888801;
a(4) = 15, 4888888888888801;
a(5) = 20, 488888888888888888801; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[(44*10^# - 791)/9] &]
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PROG
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(Magma) [n: n in [1..400] |IsPrime((44*10^n - 791) div 9)]; // Vincenzo Librandi, Dec 03 2018
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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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