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A295608
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Numbers k such that (29*10^k + 223)/9 is prime.
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0
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2, 5, 9, 11, 23, 27, 33, 111, 119, 314, 375, 551, 1694, 3413, 3495, 4172, 9287, 10412, 179697
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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 3 followed by k-2 occurrences of the digit 2 followed by the digits 47 is prime (see Example section).
a(20) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (29*10^2 + 223)/9 = 347 is prime.
Initial terms and associated primes:
a(1) = 2, 347;
a(2) = 5, 322247;
a(3) = 9, 3222222247;
a(4) = 11, 322222222247;
a(5) = 23, 322222222222222222222247; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(29*10^# + 223)/9] &]
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PROG
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(PARI) isok(k) = isprime((29*10^k + 223)/9); \\ Michel Marcus, Nov 24 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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STATUS
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approved
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