You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named butyl [4-(2,3-dichlorophenyl)-2,6-dimethyl-5-(3-methyl-1,2,4-oxadiazol-5-yl)-1,4-dihydropyridin-3-yl] carbonate by IUPAC nomenclature, provide its molecular formula.
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C21H23Cl2N3O4
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