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A293531
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Numbers k such that (268*10^k - 1)/3 is prime.
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0
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0, 2, 6, 7, 12, 13, 17, 18, 26, 77, 151, 222, 403, 567, 1107, 7221, 7722, 8475, 9729, 17904, 21404, 30170, 62523
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OFFSET
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1,2
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COMMENTS
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Numbers such that the digits 89 followed by k occurrences of the digit 3 is prime (see Example section).
a(24) > 10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (268*10^2 - 1)/3 = 8933 is prime.
Initial terms and primes associated:
a(1) = 0, 89;
a(2) = 2, 8933;
a(3) = 6, 89333333;
a(4) = 7, 893333333;
a(5) = 12, 89333333333333; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(268*10^# - 1)/3] &]
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PROG
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(PARI) isok(k) = isprime((268*10^k - 1)/3); \\ Altug Alkan, Oct 11 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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STATUS
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approved
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