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A275524
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Numbers k such that (56*10^k + 223)/9 is prime.
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0
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0, 2, 3, 5, 8, 32, 36, 53, 92, 126, 156, 158, 536, 639, 846, 1356, 1953, 2237, 4407, 5082, 17447, 17922, 24806, 25926, 29699, 30474, 37424, 63942
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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 2 followed by the digits 47 is prime (see Example section).
a(29) > 10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (56*10^3 + 223)/9 = 6247 is prime.
Initial terms and associated primes:
a(1) = 0, 31;
a(2) = 2, 647;
a(3) = 3, 6247;
a(4) = 5, 622247;
a(5) = 8, 622222247, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(56*10^# + 223)/9] &]
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PROG
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(Magma) [n: n in [0..500] | IsPrime((56*10^n+223) div 9)]; // Vincenzo Librandi, Aug 01 2016
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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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STATUS
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approved
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