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A272271
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Numbers k such that 7*10^k - 23 is prime.
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0
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1, 2, 3, 23, 29, 34, 35, 38, 52, 57, 61, 82, 186, 209, 251, 366, 394, 426, 786, 979, 1382, 2037, 4557, 8995, 12774, 19170, 21828, 23259, 32003, 41831, 44999, 56785, 76483, 97987, 110468
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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 6 followed by k-2 occurrences of the digit 9 followed by the digits 77 is prime (see Example section).
a(36) > 3*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because 7*10^3 - 23 = 6977 is prime.
Initial terms and primes associated:
a(1) = 1, 47;
a(2) = 2, 677;
a(3) = 3, 6977;
a(4) = 23, 699999999999999999999977;
a(5) = 29, 699999999999999999999999999977, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[7*10^# - 23] &]
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PROG
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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