%N Number of primitive roots Modd n (see A216321).
%C This sequence coincides with A216321 for all n values from A206551 (cyclic multiplicative Modd n group) and the entry is 0 otherwise (if no primitive root exists, that is, n is from the complementary sequence A206552).
%F a(n) = A216321(n) if n belongs to the sequence A206551 and a(n)=0 if n belongs to A206552.
%e a(8) = phi(phi(2*8)/2) = 2 , with phi = A000010, because 8 = A206551(8).
%e a(12) = 0 because 12 = A206552(1).
%Y Cf. A216321, A046144 (modulo n analog).
%A _Wolfdieter Lang_, Sep 21 2012