You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(3-chlorophenyl)-5-(1-imidazol-1-ylethyl)-3-methyl-1H-pyrazolo[1,5-a]pyrimidin-7-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H16ClN5O
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