A128678 Numbers k such that k^3 divides 4^(k^2) + 1.
1, 5, 205, 505, 20705, 40505, 168305, 408545, 1342505, 1660705, 2084645, 4091005, 10201505, 16322105, 16750345, 16998805, 37217545, 49985405, 55042705, 117165905, 135593005, 167731205, 186678805, 210549145, 218301905, 418261705
Offset: 1
Crossrefs
Programs
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Mathematica
Select[Range[5*10^6], Mod[ 4^(#^2)+1, #^3]==0 &] (* G. C. Greubel, Jan 17 2018 *)
Extensions
More terms from Ryan Propper, Jan 13 2008
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