On covering designs with block size 5 and index 11≤λ≤21: the case v≡0(mod 4)

Let V be a finite set of order v. A (v,k,A.) covering design of index A. and block size k is a collection of k-element subsets, called blocks, such that every 2-subset of V occurs in at least '}.. blocks. The covering problem is to determine the minimum number of blocks, a (v, k, A.), in a covering design. It is well known that a(v,k''}..)Lr~~=~'}..ll=(v,k,A.), where rxl is the smallest integer