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A281296
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Numbers k such that (68*10^k + 1)/3 is prime.
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0
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0, 1, 2, 8, 9, 14, 15, 20, 32, 37, 123, 134, 135, 288, 361, 414, 469, 510, 6272, 11204, 11694, 16788, 20718
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OFFSET
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1,3
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COMMENTS
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For k>0, numbers such that the digits 22 followed by k-1 occurrences of the digit 6 followed by the digit 7 is prime (see Example section).
a(24) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (68*10^2 + 1)/3 = 2267 is prime.
Initial terms and primes associated:
a(1) = 0, 23;
a(2) = 1, 227;
a(3) = 2, 2267;
a(4) = 8, 2266666667;
a(5) = 9, 22666666667; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(68*10^# + 1)/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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STATUS
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approved
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