You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[4-[4-(3-chlorophenyl)piperazin-1-yl]butyl]-3-azabicyclo[3.2.1]octane-2,4-dione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H28ClN3O2
assistant