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A282140
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Numbers k such that (49*10^k + 311)/9 is prime.
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0
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1, 3, 6, 7, 9, 10, 12, 24, 39, 135, 258, 382, 660, 900, 1306, 1528, 3658, 3937, 5157, 7006, 7936, 10956, 15396, 45808, 198403
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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 5 followed by k-2 occurrences of the digit 4 followed by the digits 79 is prime (see Example section).
a(26) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (49*10^3 + 311)/9 = 5479 is prime.
Initial terms and associated primes:
a(1) = 1, 89;
a(2) = 3, 5479;
a(3) = 6, 5444479;
a(4) = 7, 54444479;
a(5) = 9, 5444444479; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(49*10^# + 311)/9] &]
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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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