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A294945
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Numbers k such that 6*10^k - 91 is prime.
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0
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2, 6, 25, 30, 45, 98, 296, 498, 627, 1001, 1995, 1998, 2518, 3208, 3753, 4130, 7159, 7660, 10840, 16187, 24744, 28345, 31499, 32999, 44838, 60959, 88938, 209846
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OFFSET
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1,1
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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 9 followed by the digits 09 is prime (see Example section).
a(29) > 3*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because 6*10^2 - 91 = 509 is prime.
Initial terms and associated primes:
a(1) = 2, 509;
a(2) = 6, 5999909;
a(3) = 25, 59999999999999999999999909;
a(4) = 30, 5999999999999999999999999999909;
a(5) = 45, 5999999999999999999999999999999999999999999909; etc.
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MATHEMATICA
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Select[Range[2, 100000], PrimeQ[6*10^# - 91] &]
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PROG
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(PARI) isok(k) = isprime(6*10^k - 91); \\ Michel Marcus, Nov 12 2017
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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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Terms reordered into ascending order by Robert Price, Apr 03 2022
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STATUS
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approved
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