You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
tert-butyl 2-(6-chloro-3-oxo-1,2-dihydroinden-2-yl)-4-ethylpiperidine-1-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28ClNO3
assistant