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A286426
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Numbers k such that (22*10^k + 71)/3 is prime.
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0
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0, 1, 2, 6, 20, 23, 86, 146, 167, 340, 472, 500, 898, 907, 936, 1133, 2069, 3166, 4207, 5275, 9700, 20407, 28009, 32923, 53264
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OFFSET
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1,3
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COMMENTS
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For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 3 followed by the digits 57 is prime (see Example section).
a(26) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (22*10^2 + 71)/3 = 757 is prime.
Initial terms and associated primes:
a(1) = 0, 31;
a(2) = 1, 97;
a(3) = 2, 757;
a(4) = 6, 7333357;
a(5) = 20, 733333333333333333357; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(22*10^# + 71)/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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STATUS
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approved
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