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A291607
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Numbers k such that (46*10^k + 521)/9 is prime.
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0
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1, 2, 4, 5, 8, 29, 43, 62, 85, 107, 172, 557, 1043, 2395, 4498, 5818, 7772, 9125, 12616, 17252, 23000, 64904, 71077, 113162
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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 1 followed by the digits 69 is prime (see Example section).
a(25) > 2*10^5.
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LINKS
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EXAMPLE
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4 is in this sequence because (46*10^4 + 521)/9 = 51169 is prime.
Initial terms and associated primes:
a(1) = 1, 109;
a(2) = 2, 569;
a(3) = 4, 51169;
a(4) = 5, 511169;
a(5) = 8, 511111169; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(46*10^# + 521)/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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