You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-ethyl-2-[(3S)-1-[(2-methoxyphenyl)methyl]pyrrolidin-3-yl]-5-methyl-1H-pyrazolo[1,5-a]pyrimidin-7-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H26N4O2
assistant