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A128681
Numbers k such that k^3 divides 8^(k^2) + 1.
20
1, 3, 9, 57, 171, 1467, 13131, 27873, 32547, 97641, 249489, 261633, 784899, 1218897, 1255347, 2140353, 4971027, 8246019, 9961491, 12914001, 14913081, 15915483, 23159043, 23851593, 24738057, 29884473, 40666707, 83512353, 127938537
OFFSET
1,2
COMMENTS
3 divides a(n) for n > 1.
MATHEMATICA
Select[Range[5*10^6], Mod[ 8^(#^2)+1, #^3]==0 &] (* G. C. Greubel, Jan 18 2018 *)
CROSSREFS
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).
Sequence in context: A245117 A183303 A075979 * A292333 A294785 A040175
KEYWORD
hard,nonn
AUTHOR
Alexander Adamchuk, Mar 31 2007
EXTENSIONS
More terms from Ryan Propper, Jan 13 2008
STATUS
approved