You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (4-nitrophenyl)-(6-phenyl-3,5-dihydro-2H-pyrido[3,2-f][1,4]oxazepin-4-yl)methanone into its molecular formula.
user
C21H17N3O4
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