You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (6E)-6-[[1-(3-chloro-4-methoxyphenyl)-2,5-dimethylpyrrol-3-yl]methylidene]-2-ethylsulfonyl-5-imino-[1,3,4]thiadiazolo[3,2-a]pyrimidin-7-one by IUPAC nomenclature, provide its molecular formula.
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C21H20ClN5O4S2
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