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%I #15 Sep 08 2022 08:46:17
%S 3,27,267,8820000
%N Numbers n such that phi(n^2-1) = phi(n^2+1).
%C No other terms below 10^8. - _Michel Marcus_, Aug 17 2016
%e 3 is a term because phi(3^2-1) = phi(3^2+1).
%t Select[Range@10000000, EulerPhi@(#^2 - 1) == EulerPhi[#^2 + 1] &] (* _Vincenzo Librandi_, Aug 18 2016 *)
%o (PARI) isok(n) = eulerphi(n^2-1) == eulerphi(n^2+1); \\ _Michel Marcus_, Aug 16 2016
%o (Magma) [n: n in [2..100000] | EulerPhi(n^2-1) eq EulerPhi(n^2+1)]; // _Vincenzo Librandi_, Aug 18 2016
%Y Cf. A000010, A066812.
%K nonn,more
%O 1,1
%A _Altug Alkan_, Aug 16 2016
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