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A294484
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Numbers k such that 7*10^k + 69 is prime.
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0
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1, 2, 3, 6, 7, 8, 10, 12, 13, 21, 46, 68, 91, 153, 366, 1112, 1185, 1222, 7161, 20077, 33435, 40747, 99133, 108300, 136716
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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 0 followed by the digits 69 is prime (see Example section).
a(26) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because 7*10^2 + 69 = 769 is prime.
Initial terms and primes associated:
a(1) = 1, 139;
a(2) = 2, 769;
a(3) = 3, 7069;
a(4) = 6, 7000069;
a(5) = 7, 70000069; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[7*10^# + 69] &]
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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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