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A293863
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Numbers k such that (167*10^k - 17)/3 is prime.
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0
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3, 5, 13, 15, 21, 39, 45, 75, 171, 229, 293, 321, 355, 359, 1411, 2245, 3121, 8466, 9368, 40111, 102315, 126637, 173571
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OFFSET
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1,1
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COMMENTS
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For k>1, numbers such that the digits 55 followed by k-2 occurrences of the digit 6 followed by the digit 1 is prime (see Example section).
a(24) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (167*10^3 - 17)/3 = 55661 is prime.
Initial terms and primes associated:
a(1) = 3, 55661;
a(2) = 5, 5566661;
a(3) = 13, 556666666666661;
a(4) = 15, 55666666666666661;
a(5) = 21, 55666666666666666666661; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(167*10^# - 17)/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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