You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[3-(3-methoxyphenyl)-6-oxopyridazin-1-yl]-N-[2-([1,2,4]triazolo[4,3-a]pyridin-3-yl)ethyl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H20N6O3
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