Search for Covering Designs
A (v,k,t)-covering design is a collection of k-element subsets, called blocks, of {1,2,…,v}, such that any t-element subset is contained in at least one block. This site contains a collection of good (v,k,t)-coverings. Each of these coverings gives an upper bound for the corresponding C(v,k,t), the smallest possible number of blocks in such a covering design.
Search for Difference Sets
A (v,k,λ)-difference set in a group G is a subset D = {d1, d2, …, dk} of G such that each nonzero element of G can each be represented as a difference (di – dj) in exactly λ different ways.
