The pronoun object of a preposition is typically in the accusative form but may also be reflexive (e.g., She sent it to herself) or independent genitive (e.g., I hadn't heard of theirs.).
The prepositional object of a preposition is usually in the accusative form but can also be reflexive (e.g., She sent it to herself) or independent genitive (e.g., I hadn't heard of theirs).