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A274911
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Numbers k such that 7*10^k + 87 is prime.
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0
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1, 2, 5, 6, 18, 23, 59, 86, 115, 119, 251, 365, 370, 447, 1672, 3076, 3973, 5611, 7687, 8824, 13026, 17141, 17971, 23346, 29138, 94373, 94563, 142189, 156956, 255167, 266731
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section).
a(32) > 3*10^5.
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LINKS
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EXAMPLE
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5 is in this sequence because 7*10^5 + 87 = 700087 is prime.
Initial terms and associated primes:
a(1) = 1, 157;
a(2) = 2, 787;
a(3) = 5, 700087;
a(4) = 6, 7000087;
a(5) = 18, 7000000000000000087, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[7*10^# + 87] &]
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PROG
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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