You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 3-(4-ethylphenyl)-2-(6,7,8,9-tetrahydro-5H-[1,2,4]triazolo[4,3-a]azepin-3-yl)prop-2-enenitrile by IUPAC nomenclature, provide its molecular formula.
user
C18H20N4
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