You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named [(1S,2R,3S,7S,8R,9S,12S,13R,14R,15R,16R)-3,14,15-trihydroxy-2,6,13,16-tetramethyl-4,11-dioxo-10-oxatetracyclo[7.6.1.02,7.012,16]hexadec-5-en-8-yl] acetate by IUPAC nomenclature, provide its molecular formula.
user
C21H28O8
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