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A281167
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Numbers k such that (23*10^k - 143)/3 is prime.
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0
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1, 2, 6, 7, 14, 22, 31, 33, 42, 51, 799, 934, 1996, 3372, 3570, 3883, 4417, 4747, 4965, 5055, 5647, 7183, 19702, 42124, 180862, 187164
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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 19 is prime (see Example section).
a(27) > 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 - 143) / 3 = 719 is prime.
Initial terms and primes associated:
a(1) = 1, 29;
a(2) = 2, 719;
a(3) = 6, 7666619;
a(4) = 7, 76666619;
a(5) = 14, 766666666666619; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(23*10^# - 143) / 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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