You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 3-[3-[(2-chlorophenyl)methyl]-1,2,4-oxadiazol-5-yl]-7-piperidin-4-yl-2,3,3a,4-tetrahydro-1H-pyrazolo[1,5-a]pyrimidin-5-one by IUPAC nomenclature, provide its molecular formula.
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C20H23ClN6O2
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