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A046430
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All the prime factors of repunit a(n) end with the digit 1.
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1
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1, 2, 4, 5, 10, 19, 20, 23, 25, 38, 50, 59, 76, 95, 100, 115, 125, 190, 250, 295, 317, 380
(list;
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listen;
history;
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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)=10 -> 11*41*271*9091 ->1(1)*4(1)*27(1)*909(1).
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MATHEMATICA
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Select[Range[60], Length[fi=FactorInteger[(10^#-1)/9]]==Length[Select[First/@fi, Mod[#, 10]==1&]] &](* Ray Chandler, Apr 24 2017 *)
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CROSSREFS
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KEYWORD
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nonn,more,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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