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A282815
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Numbers k such that (28*10^k + 131)/3 is prime.
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0
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0, 1, 2, 3, 4, 8, 19, 100, 162, 228, 405, 535, 548, 1616, 1982, 2139, 2832, 3115, 3750, 4767, 5051, 9970, 15708, 20909, 33755, 41669, 44822, 45638, 75078
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OFFSET
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1,3
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COMMENTS
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For k>1, numbers such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 77 is prime (see Example section).
a(30) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (28*10^3 + 131)/3 = 9377 is prime.
Initial terms and primes associated:
a(1) = 0, 53;
a(2) = 1, 137;
a(3) = 2, 977;
a(4) = 3, 9377;
a(5) = 4, 93377; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(28*10^# + 131)/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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