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A046420
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Prime factors of repunit of length a(n) are all of different lengths.
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2
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1, 2, 3, 4, 5, 7, 11, 14, 17, 19, 23, 31, 34, 37, 38, 41, 43, 47, 49, 51, 53, 57, 59, 62, 67, 69, 71, 73, 74, 79, 83, 85, 86, 89, 93, 94, 97, 101, 103, 106, 109, 113, 115, 118, 119, 129, 134, 137, 139, 141, 142, 146, 149, 151, 157, 159, 163
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OFFSET
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1,2
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LINKS
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Eric Weisstein's World of Mathematics, Repunit
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EXAMPLE
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a(n)=14 -> 11*239*4649*909091 -> (2)(3)(4)(6) all of different lengths.
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MATHEMATICA
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Select[Range[60], Length[fi=FactorInteger[(10^#-1)/9]]== Plus@@Last/@fi==Length[Union[IntegerLength/@First/@fi]]&] (* Ray Chandler, Apr 24 2017 *)
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CROSSREFS
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KEYWORD
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nonn,base,changed
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AUTHOR
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EXTENSIONS
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Offset changed to 1 and more terms added by Ray Chandler, Apr 24 2017
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STATUS
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approved
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