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A294121
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Numbers k such that (8*10^k - 101)/3 is prime.
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0
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2, 3, 4, 5, 6, 17, 53, 95, 156, 228, 261, 323, 363, 1208, 1733, 1744, 2207, 15728, 18196, 50750, 66261, 83811, 156718
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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 2 followed by k-2 occurrences of the digit 6 followed by the digits 33 is prime (see Example section).
a(24) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (8*10^3 - 101)/3 = 2633 is prime.
Initial terms and associated primes:
a(1) = 2, 233;
a(2) = 3, 2633;
a(3) = 4, 26633;
a(4) = 5, 266633;
a(5) = 6, 2666633; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[(8*10^# - 101)/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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