67147431domain: NAppears in sequencesNumber of n X n binary matrices M (that is, real matrices with entries 0 and 1) such that M^2 is also a binary matrix.at n=6A121231Duplicate of A121231.at n=5A122527T(n,k)=Number of n X n 0..k matrices whose square is also a 0..k matrix.at n=20A213990