You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-[4-[4-(1-butan-2-yl-5-oxo-1,2,4-triazol-4-yl)phenyl]piperazin-1-yl]-1H-pyridin-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H26N6O2
assistant