You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 2-[(2-ethyl-5,6,7,8-tetrahydro-[1,2,4]triazolo[1,5-a]pyridin-6-yl)amino]pyridine-3-carboxylate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C16H21N5O2
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