You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[(1R)-1-(2-methoxy-5-methylphenyl)ethyl]-3-phenyl-[1,2,4]triazolo[4,3-b]pyridazin-6-amine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21N5O
assistant