You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (1R,9S)-4,5,13-trimethoxy-12-oxo-17-azatetracyclo[7.5.3.01,10.02,7]heptadeca-2,4,6,10,13-pentaene-17-carbaldehyde by IUPAC nomenclature, provide its molecular formula.
user
C20H21NO5
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