You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named N-(1,3-benzothiazol-2-yl)-2-[3-(2,4-dimethoxyphenyl)-6-oxopyridazin-1-yl]acetamide by IUPAC nomenclature, provide its molecular formula.
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C21H18N4O4S
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