Representations for the Drazin inverses of the sum of two matrices and some block matrices

In this paper, we give some formulas of the Drazin inverses of the sum of two matrices under the conditions P2Q=0,Q2P=0 and P3Q=0,QPQ=0,QP2Q=0 respectively. And we also give some representations for the Drazin inverse of block matrix ABCD (A and D are square) under some conditions.