You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (2R)-2-[(S)-hydroxy-[1-[(2-methylphenyl)methyl]pyridin-1-ium-4-yl]methyl]-2,3-dihydropyrrolizin-1-one into its molecular formula.
user
C21H21N2O2+
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