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 A128681 #11 Jun 08 2021 02:22:46 %S A128681 1,3,9,57,171,1467,13131,27873,32547,97641,249489,261633,784899, %T A128681 1218897,1255347,2140353,4971027,8246019,9961491,12914001,14913081, %U A128681 15915483,23159043,23851593,24738057,29884473,40666707,83512353,127938537 %N A128681 Numbers k such that k^3 divides 8^(k^2) + 1. %C A128681 3 divides a(n) for n > 1. %t A128681 Select[Range[5*10^6], Mod[ 8^(#^2)+1, #^3]==0 &] (* _G. C. Greubel_, Jan 18 2018 *) %Y A128681 Cf. A127263 (numbers k such that k^3 divide 2^(k^2)+1). %Y A128681 Cf. A128677 (least k > p such that (k*p)^3 divides (p-1)^(k*p)^2+1, where p = prime(n) > 2). %Y A128681 Cf. A128678, A128679, A128680, A128682, A128683, A128684, A128685. %K A128681 hard,nonn %O A128681 1,2 %A A128681 _Alexander Adamchuk_, Mar 31 2007 %E A128681 More terms from _Ryan Propper_, Jan 13 2008