pub fn galois_group(n: usize) -> Vec<u64>
The n = φ(2n) Galois automorphisms of R = ℤ[X]/(Xⁿ+1), as the odd residues mod 2n that index them.
n = φ(2n)
R = ℤ[X]/(Xⁿ+1)
2n