You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(3-chloro-2-methylphenyl)-6-methyl-2-(4-pyridin-2-ylpiperazin-1-yl)pyrimidin-4-amine is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H23ClN6
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