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A279050
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Numbers k such that (14*10^k - 143)/3 is prime.
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0
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2, 4, 5, 11, 23, 27, 28, 60, 114, 154, 160, 194, 412, 417, 769, 1189, 3845, 5381, 10905, 11192, 11630, 19737, 56080, 155740, 259431, 282673
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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 6 followed by the digits 19 is prime (see Example section).
a(27) > 3*10^5.
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LINKS
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EXAMPLE
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4 is in this sequence because (14*10^4 - 143) / 3 = 46619 is prime.
Initial terms and associated primes:
a(1) = 2, 419;
a(2) = 4, 46619;
a(3) = 5, 466619;
a(4) = 11, 466666666619;
a(5) = 23, 466666666666666666666619; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[(14*10^# - 143) / 3] &]
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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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