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 A218766 #19 Feb 16 2025 08:33:18
%S A218766 289,841,3721,4913,9409,11881,12769,22201,24389,32761,37249,52441,
%T A218766 54289,66049,72361,83521,97969,113569,151321,187489,212521,226981,
%U A218766 259081,292681,332929,351649,491401,502681,674041,707281,734449,877969,885481,908209,912673
%N A218766 Composite numbers with both 10 and -10 as primitive root.
%C A218766 The powers of primes from A007349.
%C A218766 Intersection of A002808, A167797 and A167806.
%H A218766 Arkadiusz Wesolowski, <a href="/A218766/b218766.txt">Table of n, a(n) for n = 1..10000</a>
%H A218766 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PrimitiveRoot.html">Primitive Root</a>
%e A218766 12769 = 113^2 belongs to this sequence because 113 is in A007349.
%t A218766 lst = {}; r = 912673; Do[If[PrimeQ[i] && MultiplicativeOrder[10, i] == MultiplicativeOrder[-10, i] == i - 1, n = 2; While[(p = i^n) <= r, AppendTo[lst, p]; n++]], {i, Floor@Sqrt[r]}]; Sort[lst]
%Y A218766 Cf. A007349.
%K A218766 nonn
%O A218766 1,1
%A A218766 _Arkadiusz Wesolowski_, Nov 05 2012