You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-[3a-[(5,6-dimethylpyrimidin-4-yl)oxymethyl]-1,3,4,5,6,6a-hexahydrocyclopenta[c]pyrrol-2-yl]-9-methylpurine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H25N7O
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