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A293591
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Numbers k such that (7*10^k + 113)/3 is prime.
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0
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1, 2, 3, 4, 5, 8, 18, 30, 95, 165, 805, 2738, 3038, 5953, 6009, 7205, 9631, 17495, 27745, 28449, 62278, 106516, 130825, 153664
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OFFSET
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1,2
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COMMENTS
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For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 3 followed by the digits 71 is prime (see Example section).
a(25) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (7*10^2 + 113)/3 = 271 is prime.
Initial terms and primes associated:
a(1) = 1, 61;
a(2) = 2, 271;
a(3) = 3, 2371;
a(4) = 4, 23371;
a(5) = 5, 233371; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(7*10^# + 113)/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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