You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-(4-butylphenyl)-3-chloro-4-[methyl-(1-methylpiperidin-4-yl)amino]pyrrole-2,5-dione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H28ClN3O2
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