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A108966
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Numbers n such that repunit(n) concatenated with its 10's complement is prime; or numbers n such that (1+7*10^n+100^n)/9 is prime.
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1
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1, 5, 16, 36, 61, 149, 725, 1104, 1276, 1289, 8575
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OFFSET
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1,2
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COMMENTS
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Larger values are only Fermat and Lucas PRPs.
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LINKS
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EXAMPLE
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a(2)=5 because 10^5-11111 = 88889 and 1111188889 is prime.
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CROSSREFS
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KEYWORD
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base,hard,more,nonn
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AUTHOR
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STATUS
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approved
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