You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
tert-butyl (3S,6R,7S,8S)-9-butoxy-3,7-dihydroxy-4,4,6,8-tetramethyl-5-oxononanoate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H40O6
assistant