You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named methyl (1R,2R,3S,12bR)-1-nitro-4-oxo-2-phenyl-2,3,6,7,12,12b-hexahydro-1H-indolo[2,3-a]quinolizine-3-carboxylate by IUPAC nomenclature, provide its molecular formula.
user
C23H21N3O5
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