On (0,1)-matrix semigroups

In this paper we count the number of elements and idempotents in certainD-classes of the semigroup B_n of all binary relations on a set of n elements, namely whose those row and column rank do not exceed 3. This is an announcement of the results; detailed proofs of all results are contained in [2]. The author presented the abstract of this paper in person at Tacoma, Washington, the 676 Meeting of the Amer. Math. Soc., June 20, 1970.