You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named [4-(3-chloro-1-benzothiophene-2-carbonyl)piperazin-1-yl]-[2-(difluoromethoxy)phenyl]methanone by IUPAC nomenclature, provide its molecular formula.
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C21H17ClF2N2O3S
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