You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-[(4,5-dimethylpyridin-2-yl)methyl]-2-(phenoxymethyl)-6,7-dihydropyrazolo[1,5-a]pyrazin-4-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H22N4O2
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