209430787824domain: NAppears in sequencesNumber of n-bead necklaces with 4 colors.at n=21A001868An intermediate sequence for nonisomorphic circulant undirected p^2-graphs, indexed by odd primes p.at n=12A038783Number of distinct n X 3 toroidal 0..3 arrays.at n=6A184274a(n) = -(1/n) * Sum_{d|n} phi(n/d) * (-4)^d.at n=20A343466