979776000domain: NAppears in sequencesNumber of n X n binary matrices with no 0 rows or columns and with n+1 1's.at n=9A055602a(n) is the number of solutions to the congruence Sum_{k=1..n} x_k == 1 (mod 2n), where x_k are distinct elements of the set {0, 1, ..., 2n}, k = 1..n.at n=8A174663