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First of 4 or more consecutive integers with equal values of phi(phi(n)).
2

%I #29 Jul 19 2017 08:53:10

%S 1,7,31,32,2694,131071,50802031105

%N First of 4 or more consecutive integers with equal values of phi(phi(n)).

%C Next term > 1266046940 (last term of A167767 b-file). - _Michel Marcus_, Jun 23 2013

%C No other terms < 1.32*10^12. - _Jud McCranie_, Jul 19 2017

%e p2(1) = p2(2) = p2(3) = p2(4) = 1, p2(7) = p2(8) = p2(9) = p2(10) = 2.

%t a[n_] := EulerPhi[EulerPhi[n]]; Select[Range[10000], a[#] == a[# + 1] && a[# + 1] == a[# + 2] && a[# + 2] == a[# + 3] &] (* _G. C. Greubel_, Jun 23 2016 *)

%o (PARI) pp(n) = eulerphi(eulerphi(n))

%o isA167768(n) = pp(n)==pp(n+1) && pp(n+1)==pp(n+2) && pp(n+2)==pp(n+3) \\ _Michael B. Porter_, Nov 24 2009

%Y Cf. A167767 (of which this list is a subset), A167766.

%K more,nonn,hard

%O 1,2

%A _Fred Schneider_, Nov 11 2009

%E Edited by _N. J. A. Sloane_, Nov 12 2009

%E a(7) added by _Jud McCranie_, Jul 17 2017