244648domain: NAppears in sequencesa(n) = 441*n^2 - 394*n + 88.at n=23A157734Table read by antidiagonals: T(n,k) is the number of idempotent n X n 0..k matrices of rank 1.at n=43A224524Sum of the k-th arithmetic derivative of n-k for k=0..n.at n=21A258652