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A294631
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Numbers k such that (59*10^k - 77)/9 is prime.
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0
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2, 3, 5, 6, 9, 14, 21, 29, 30, 32, 39, 59, 69, 113, 410, 13484, 15525, 16796, 22064, 37694, 38103, 73217
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OFFSET
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1,1
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COMMENTS
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For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 5 followed by the digits 47 is prime (see Example section).
a(23) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (59*10^2 - 77)/9 = 647 is prime.
Initial terms and primes associated:
a(1) = 2, 647;
a(2) = 3, 6547;
a(3) = 5, 655547;
a(4) = 6, 6555547;
a(5) = 9, 6555555547; etc.
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MATHEMATICA
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Select[Range[1, 100000], PrimeQ[(59*10^# - 77)/9] &]
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PROG
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(PARI) is(n) = ispseudoprime((59*10^n - 77)/9) \\ Felix Fröhlich, May 30 2019
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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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