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 A319383 #28 Oct 09 2020 19:52:02
%S A319383 1,2,19043,289627,6674419,49865347,185014655
%N A319383 Numbers k such that phi(k)^phi(k) == 1 (mod k^2).
%C A319383 All terms are cyclic numbers (A003277).
%C A319383 The next term, if it exists, is > 10^10. - _Vaclav Kotesovec_, Oct 23 2018
%C A319383 a(8) > 10^12, if it exists. - _Giovanni Resta_, Oct 25 2018
%t A319383 Select[Range[20000], Divisible[EulerPhi[#]^EulerPhi[#] - 1, #^2] &] (* _Vaclav Kotesovec_, Oct 21 2018 *)
%t A319383 Join[{1},Select[Range[1851*10^5],With[{c=EulerPhi[#]},PowerMod[c,c,#^2] == 1&]]] (* _Harvey P. Dale_, Oct 09 2020 *)
%o A319383 (PARI) isok(n) = Mod(eulerphi(n), n^2)^eulerphi(n)==1;
%o A319383 for(n=1, 10000000, if(isok(n),print1(n, ", ")))
%Y A319383 Cf. A000010, A003277, A063439, A077816.
%K A319383 nonn,more
%O A319383 1,2
%A A319383 _Altug Alkan_, Sep 18 2018