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A293856
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Numbers k such that (32*10^k + 319)/9 is prime.
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0
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1, 4, 5, 7, 8, 10, 14, 20, 44, 76, 88, 110, 121, 1469, 1535, 5030, 16391, 19592, 25265, 25819, 54458, 68320
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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 3 followed by k-2 occurrences of the digit 5 followed by the digits 91 is prime (see Example section).
a(23) > 2*10^5.
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LINKS
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EXAMPLE
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4 is in this sequence because (32*10^4 + 319)/9 = 35591 is prime.
Initial terms and primes associated:
a(1) = 1, 71;
a(2) = 4, 35591;
a(3) = 5, 355591;
a(4) = 7, 35555591;
a(5) = 8, 355555591; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(32*10^# + 319)/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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STATUS
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approved
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