Constructive covers of a finite set

Çağın Ararat, Ülkü Gürler, M. Emrullah Ildız

Given positive integers $n,k$ with $k\le n$, we consider the number of ways of choosing $k$ subsets of $\{1,\dots ,n\}$ in such a way that the union of these subsets gives $\{1,\l…