You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named N-(2-chlorophenyl)-3-(2-methoxyethyl)spiro[5,6,8,9-tetrahydro-[1,2,4]triazolo[4,3-a]azepine-7,4'-piperidine]-1'-carboxamide by IUPAC nomenclature, provide its molecular formula.
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C21H28ClN5O2
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