You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 4-chloro-5-[4-(3,3-dimethylbutanoyl)piperazin-1-yl]-2-phenylpyridazin-3-one by IUPAC nomenclature, provide its molecular formula.
user
C20H25ClN4O2
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