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Under IUPAC nomenclature, a molecule named 1-[(2R,5R)-1-[2-(6-chloro-3,3-dimethyl-2H-indol-1-yl)-2-oxoethyl]-5-methylpiperazin-2-yl]propan-1-one is given. What is its corresponding molecular formula?
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C20H28ClN3O2
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