You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
7-methyl-8-(1-methylpyridin-1-ium-2-yl)-3-(1,1,1,2-tetradeuteriopropan-2-yl)-[1]benzofuro[3,2-c]pyridine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21N2O+
assistant