This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A128678 #14 Jun 08 2021 02:22:56 %S A128678 1,5,205,505,20705,40505,168305,408545,1342505,1660705,2084645, %T A128678 4091005,10201505,16322105,16750345,16998805,37217545,49985405, %U A128678 55042705,117165905,135593005,167731205,186678805,210549145,218301905,418261705 %N A128678 Numbers k such that k^3 divides 4^(k^2) + 1. %C A128678 5 divides a(n) for n > 1. %t A128678 Select[Range[5*10^6], Mod[ 4^(#^2)+1, #^3]==0 &] (* _G. C. Greubel_, Jan 17 2018 *) %Y A128678 Cf. A127263, A128677, A128679, A128680, A128681, A128682, A128683, A128684, A128685, A292330. %K A128678 hard,nonn %O A128678 1,2 %A A128678 _Alexander Adamchuk_, Mar 31 2007 %E A128678 More terms from _Ryan Propper_, Jan 13 2008