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 A241978 #18 Jan 27 2020 07:47:21 %S A241978 66161,330805,534851,2674255,3152573,10162169,13371275,50810845, %T A241978 54715147,129255493,148170931,254054225,273575735,301121113,383006029, %U A241978 646277465,1289402357,1505605565,1915030145,3228193673,3407931413,5721301147,6075008171,7528027825 %N A241978 Numbers n such that 6^phi(n) == 1 (modulo n^2), where phi(n) is Euler's totient function. %C A241978 a(17) > 10^9. %H A241978 Giovanni Resta, <a href="/A241978/b241978.txt">Table of n, a(n) for n = 1..95</a> (terms < 10^14) %t A241978 Select[Range[65*10^7],PowerMod[6,EulerPhi[#],#^2]==1&] (* _Harvey P. Dale_, Jan 20 2020 *) %o A241978 (PARI) for(n=2, 1e9, if(Mod(6, n^2)^(eulerphi(n))==1, print1(n, ", "))) %Y A241978 Cf. A000010, A077816, A212583, A242958, A242959, A242960, A241977, A245529. %K A241978 nonn %O A241978 1,1 %A A241978 _Felix Fröhlich_, Aug 10 2014 %E A241978 Terms a(17) and beyond from _Giovanni Resta_, Jan 24 2020