%N Numbers k such that (Z/mZ)* = C_2 X C_(2k) has no solutions m, where (Z/mZ)* is the multiplicative group of integers modulo m..
%C Indices of 0 in A328410, A328411 and A328412.
%C By definition, if there is no such m that psi(m) = 2k, psi = A002322, then m is a term of this sequence.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Multiplicative_group_of_integers_modulo_n">Multiplicative group of integers modulo n</a>
%e 12 is a term: if there exists m such that (Z/mZ)* = C_2 X C_24 = C_2 X C_8 X C_3, then m must have a factor q such that q is an odd prime power and phi(q) = 8 or phi(q) = 24, phi = A000010, which is impossible.
%e 80 is a term: if there exists m such that (Z/mZ)* = C_2 X C_80 = C_2 X C_16 X C_5, then m must have a factor q such that q is an odd prime power and phi(q) = 80 or phi(q) = 16, which is impossible.
%o (PARI) isA328414(n) = my(r=4*n, N=floor(exp(Euler)*r*log(log(r^2))+2.5*r/log(log(r^2)))); for(k=r+1, N+1, if(eulerphi(k)==r && lcm(znstar(k))==r/2, return(0)); if(k==N+1, return(1)))
%o for(n=1, 200, if(isA328414(n), print1(n, ", ")))
%Y Cf. A328410, A328411, A328412. Complement of A328413.
%Y Cf. also A000010, A002322, A005277, A079695.
%A _Jianing Song_, Oct 14 2019