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A282138
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Numbers k such that (19*10^k - 49)/3 is prime.
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0
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1, 2, 3, 4, 5, 6, 7, 21, 22, 101, 111, 132, 174, 201, 265, 335, 388, 537, 1011, 1012, 1254, 6766, 20236, 55833, 104014, 134786, 146181, 159921, 210011
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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 6 followed by k-2 occurrences of the digit 3 followed by the digits 17 is prime (see Example section).
a(30) > 3*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (19*10^3 - 49)/3 = 6317 is prime.
Initial terms and associated primes:
a(1) = 1, 47;
a(2) = 2, 617;
a(3) = 3, 6317;
a(4) = 4, 63317;
a(5) = 5, 633317; etc.
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MATHEMATICA
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Select[Range[1, 100000], PrimeQ[(19*10^# - 49)/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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