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phi(n) is equal to the product of the dual prime-power components of n-1 (i.e., A008477(n-1)).
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%I #10 Aug 03 2017 01:29:02

%S 5,17,51,73,109,433,17408,21601,121501,1350001,3294173,9376762501

%N phi(n) is equal to the product of the dual prime-power components of n-1 (i.e., A008477(n-1)).

%C a(13) > 3*10^10. - _Donovan Johnson_

%e phi(17408) = 8192, 17407 = 13^2*103^1, (2^13)*(1^103) = 8192.

%Y Cf. A000010, A008477.

%K nonn

%O 1,1

%A _Olivier GĂ©rard_

%E More terms from _Naohiro Nomoto_, Jun 24 2001

%E a(12) from _Donovan Johnson_, Nov 14 2010