You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 18-methyl-3,13,21-triazapentacyclo[11.8.0.02,10.04,9.015,20]henicosa-1(21),2(10),4(9),5,15(20),16,18-heptaen-14-one by IUPAC nomenclature, provide its molecular formula.
user
C19H17N3O
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