498112275domain: NAppears in sequencesNumber of n-bead necklaces with 3 colors.at n=21A001867Number of distinct n X 3 toroidal 0..2 arrays.at n=6A184280Table read by antidiagonals: T(n,k) = number of distinct n X k toroidal 0..2 arrays.at n=38A184284a(n) = -(1/n) * Sum_{d|n} phi(n/d) * (-3)^d.at n=20A343465