You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5,11-bis[(4-aminophenyl)methyl]-3,5,7,9,11,13-hexazatricyclo[8.3.0.02,6]trideca-1(10),2,6,8,12-pentaen-4-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H18N8O
assistant