Full Idea
In classical mereology, if there are c atoms, where c is any cardinal number, there are 2^c - 1 individuals, so the cardinality of models is restricted. There are no models with cardinality 2, 12 or aleph-0, for example.
Gist of Idea
If there are c atoms, this gives 2^c - 1 individuals, so there can't be just 2 or 12 individuals
Source
Peter Simons (Parts [1987], 1.2)
Book Reference
Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.17
A Reaction
The news that there is no possible world containing just 2 or just 12 individuals ought to worry fans of extensional mereology. A nice challenge for God - create a world containing just 12 individuals.