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Numbers n for which phi(n^2) = phi(n-1) * phi(n+1).
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%I #14 Aug 12 2019 13:58:54

%S 2,4,16,256,976,3256,5188,11716,13366,22936,65536,307396,491536,

%T 589408,983776,1659586,2822716,3137356,5577826,6475456,7378372,

%U 8698096,10798726,32235736,37797436,39220126,39285436,51555136,52077196,56992552,63767926,70075996,82391002

%N Numbers n for which phi(n^2) = phi(n-1) * phi(n+1).

%e phi(976^2) = 468480 = 480*976 = phi(975)*phi(977).

%t Select[Range[10^6], EulerPhi[#^2] == EulerPhi[# - 1] EulerPhi[# + 1] &]

%o (PARI) isok(n) = eulerphi(n^2) == eulerphi(n-1) * eulerphi(n+1); \\ _Michel Marcus_, Aug 12 2019

%Y Cf. A000010, A076529, A220160.

%K nonn

%O 1,1

%A _Carl Najafi_, Dec 06 2012

%E More terms from _Amiram Eldar_, Aug 12 2019