You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 5-ethyl-N-[[6-[2-(2H-tetrazol-5-yl)phenyl]pyridin-3-yl]methyl]pyrazolo[1,5-a]pyrimidin-7-amine into its molecular formula.
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C21H19N9
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