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system
Name the molecular formula for the molecule established as 1-[(6aR,10aR)-5-bromo-7,9-dimethyl-6,6a,8,10a-tetrahydroindolo[4,3-fg]quinolin-4-yl]-2,2-dimethylpropan-1-one using the IUPAC nomenclature.
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C21H25BrN2O
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