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A067063
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Smallest prime factor of repunit(n) = (10^n-1)/9 (A002275).
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13
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11, 3, 11, 41, 3, 239, 11, 3, 11, 21649, 3, 53, 11, 3, 11, 2071723, 3, 1111111111111111111, 11, 3, 11, 11111111111111111111111, 3, 41, 11, 3, 11, 3191, 3, 2791, 11, 3, 11, 41, 3, 2028119, 11, 3, 11, 83, 3, 173, 11, 3, 11, 35121409, 3, 239
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OFFSET
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2,1
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COMMENTS
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REFERENCES
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David Wells, The Penguin Dictionary of Curious and Interesting Numbers.
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LINKS
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FORMULA
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a(3n) = 3, a(6n-4) = a(6n-2) = 11, a(30n-25) = a(30n-5) = 41, ... - M. F. Hasler, Nov 21 2006
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MAPLE
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'min(op(numtheory[factorset]((10^k-1)/9)))'$k=2..50; # M. F. Hasler, Nov 21 2006
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MATHEMATICA
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a = {}; Do[a = Append[a, FactorInteger[(10^n - 1)/9][[1, 1]]], {n, 2, 111} ]; a
Table[FactorInteger[FromDigits[PadRight[{}, n, 1]]][[1, 1]], {n, 2, 50}] (* Harvey P. Dale, Dec 10 2013 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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