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Under IUPAC nomenclature, a molecule named (8bS)-8b-[(8bS)-2,3,3a,4-tetrahydro-1H-pyrrolo[2,3-b]indol-8b-yl]-3-methyl-1,2,3a,4-tetrahydropyrrolo[2,3-b]indole is given. What is its corresponding molecular formula?
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C21H24N4
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