Directed covering with block size 5 and index even Original Research Article

A directed covering design, DC(v,k,λ), is a (v,k,2λ) covering design in which the blocks are regarded as ordered k-tuples and in which each ordered pair of elements occurs in at least λ blocks. Let DE(v,k,λ) denote the minimum number of blocks in a DC(v,k,λ). In this paper the values of the function DE(v,5,λ) are determined for all positive integers v ⩾ 5 and λ even.