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For the molecule named 2-[(1R,3S,3aR,6aS)-5'-bromo-5-tert-butyl-2',4,6-trioxospiro[1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrole-3,3'-1H-indole]-1-yl]acetamide by IUPAC nomenclature, provide its molecular formula.
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C19H21BrN4O4
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