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A275522
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Numbers k such that (28*10^k + 773)/9 is prime.
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0
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0, 2, 5, 6, 11, 20, 32, 59, 81, 98, 128, 437, 758, 989, 998, 1403, 1548, 1907, 1914, 2219, 5414, 9047, 13196, 18518, 28382
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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 3 followed by k-2 occurrences of the digit 1 followed by the digits 97 is prime (see Example section).
a(26) > 10^5.
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LINKS
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EXAMPLE
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5 is in this sequence because (28*10^5 + 773)/9 = 311197 is prime.
Initial terms and associated primes:
a(1) = 0, 89;
a(2) = 2, 397;
a(3) = 5, 311197;
a(4) = 6, 3111197;
a(5) = 11, 311111111197, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(28*10^# + 773)/9] &]
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PROG
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(Magma) [n: n in [0..500] | IsPrime((28*10^n+773) div 9)]; // Vincenzo Librandi, Aug 01 2016
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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