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A294485
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Numbers k such that (23*10^k + 19)/3 is prime.
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0
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1, 2, 3, 4, 9, 10, 11, 17, 95, 115, 499, 1048, 1557, 3392, 4841, 5174, 11427, 12044, 14984, 16747, 38936, 44492, 110290, 149655
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OFFSET
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1,2
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COMMENTS
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For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 6 followed by the digits 73 is prime (see Example section).
a(25) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (23*10^2 + 19)/3 = 773 is prime.
Initial terms and primes associated:
a(1) = 1, 83;
a(2) = 2, 773;
a(3) = 3, 7673;
a(4) = 4, 76673;
a(5) = 9, 7666666673; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(23*10^# + 19)/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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