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A295322
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Numbers k such that (17*10^k - 377)/9 is prime.
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0
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3, 19, 27, 145, 166, 196, 247, 345, 370, 799, 1093, 2877, 5223, 9157, 22927, 24600, 25546, 29424, 82540, 95451, 159438
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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 1 followed by k-2 occurrences of the digit 8 followed by the digits 47 is prime (see Example section).
a(22) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (17*10^3 - 377)/9 = 1847 is prime.
Initial terms and associated primes:
a(1) = 3, 1847;
a(2) = 19, 18888888888888888847;
a(3) = 27, 1888888888888888888888888847; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[(17*10^# - 377)/9] &]
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PROG
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(PARI) isok(k) = isprime((17*10^k - 377)/9); \\ Michel Marcus, Nov 20 2017
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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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