You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-[4-chloro-3-(2,3-dihydro-1-benzofuran-5-ylmethyl)phenyl]-4-hydroxy-2-(hydroxymethyl)oxan-3-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21ClO5
assistant