Fig. 1

Grouping (by colour) of: even, odd non-prime, and prime numerosities. In this example, it is possible to see how, in line with what hypothesized by Welling, one can visually disassemble composite numerosities into same-sized subsets, but the same is not true for prime numerosities, which will always result in at least one subgroup being of a different numerosity. Here elements are grouped by colour, but it is possible to obtain the same result employing other grouping strategies based on Gestalt principles, such as shape similarity or spatial proximity