You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule (7a-methyl-4-pyridin-3-yl-1,7-dihydropyrrolo[2,3-b]pyridin-3-yl)-(2-methylphenyl)methanone ?
user
C21H19N3O
assistant