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A128680
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Numbers k such that k^3 divides 6^(k^2) + 1.
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20
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1, 7, 203, 1379, 11977, 39991, 577129, 2359469, 4780447, 6521291, 6640739, 9904979, 21511301, 28434413, 34050611, 113694413, 189117439, 222281549, 250163599, 282046373, 391803601, 941748059, 1269166759, 1308225583
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OFFSET
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1,2
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COMMENTS
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7 divides a(n) for n > 1.
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LINKS
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MATHEMATICA
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Select[Range[5*10^6], Mod[ 6^(#^2)+1, #^3]==0 &] (* G. C. Greubel, Jan 18 2018 *)
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CROSSREFS
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Cf. A127263 (numbers k such that k^3 divide 2^(k^2)+1).
Cf. A128677 (least k > p such that (k*p)^3 divides (p-1)^(k*p)^2+1, where p = prime(n) > 2).
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KEYWORD
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hard,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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