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A216530
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Numbers n such that 10^n+1 can be written in the form a^2+7*b^2.
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0
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1, 7, 19, 31, 49, 61, 67, 109, 133, 139, 157, 163, 211, 217
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OFFSET
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1,2
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COMMENTS
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These numbers of the form 10^n+1 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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