138096domain: NAppears in sequencesRed rooted red-black trees with n internal nodes.at n=21A001138Numbers n such that determinant[{{n,phi(n)},{n+1,phi(n+1)}}]is a perfect square.at n=20A067571Number of subsets of {1,...,n} not containing {a,a+2,a+4} for any a.at n=19A209410