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A216527
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Odd numbers n such that (10^n-1)/9 can be written in the form a^2+7*b^2.
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0
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1, 7, 13, 19, 23, 37, 47, 49, 53, 59, 71, 73, 83, 91, 101, 103, 127, 133, 149, 151, 161, 191, 211, 259, 266, 317, 329
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OFFSET
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1,2
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COMMENTS
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These repunit numbers of the form (10^n-1)/9 have no prime factors congruent to 3 (mod 7) or 5 (mod 7) or 6 (mod 7) to an odd power. Also the power of 2 is not 1.
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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