You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-(5-ethyl-2-methylpyridin-1-ium-1-yl)-1-(2-methyl-1H-indol-3-yl)ethanone by IUPAC nomenclature, provide its molecular formula.
user
C19H21N2O+
assistant