You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[[(1R)-1,7-dimethyl-3-oxo-1,2-dihydroinden-4-yl]oxy]-N-[(1R)-1-(4-fluorophenyl)ethyl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H22FNO3
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