Published online by Cambridge University Press: 20 November 2018
Let $D$ be a family of
$k$-subsets (called blocks) of a
$v$-set
$X\left( v \right)$. Then
$D$ is a
$\left( v,\,k,\,t \right)$ covering design or covering if every
$t$-subset of
$X\left( v \right)$ is contained in at least one block of
$D$. The number of blocks is the size of the covering, and the minimum size of the covering is called the covering number. In this paper we consider the case
$t\,=\,2$, and find several infinite classes of covering numbers. We also give upper bounds on other classes of covering numbers.
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