You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1H-indol-2-yl-[4-(5-phenyl-1,2,4-oxadiazol-3-yl)piperazin-1-yl]methanone The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H19N5O2
assistant