Wegner gave a geometric characterization of all so-called Groemer packing of n >= 2 unit discs in E-2 that are densest packings of n unit discs with respect to the convex hull of the discs. In this paper we provide a number theoretic characterization of all n satisfying that such a "Wegner packing" of n unit discs exists, and show that the proportion of these n is 23/24 among all natural numbers.