You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (3-methoxyphenyl)-[4-(4-methylsulfonyl-1,3-benzothiazol-2-yl)piperazin-1-yl]methanone by IUPAC nomenclature, provide its molecular formula.
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C20H21N3O4S2
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