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A282895
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Numbers k such that (11*10^k + 91)/3 is prime.
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0
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1, 2, 3, 4, 5, 7, 9, 15, 27, 29, 39, 62, 77, 106, 114, 357, 555, 962, 1013, 2372, 8235, 16047, 82323, 294308
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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 3 followed by k-2 occurrences of the digit 6 followed by the digits 97 is prime (see Example section).
a(25) > 3*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (11*10^3 + 91)/3 = 3697 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 2, 397;
a(3) = 3, 3697;
a(4) = 4, 36697;
a(5) = 5, 366697; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(11*10^# + 91)/3] &]
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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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