You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named N-[(5-ethylthiophen-2-yl)methyl]-2-[3-(6,7,8,9-tetrahydro-5H-[1,2,4]triazolo[4,3-a]azepin-3-yl)piperidin-1-yl]acetamide by IUPAC nomenclature, provide its molecular formula.
user
C21H31N5OS
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