You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(8R)-6-[(E)-(3-chlorophenyl)methylideneamino]-3,6,17-triazatetracyclo[8.7.0.03,8.011,16]heptadeca-1(10),11,13,15-tetraene-4,7-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H17ClN4O2
assistant