You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (2R,6S)-4-(2,6-diethyl-4-methylphenyl)-5-methoxy-10-oxatricyclo[5.2.1.02,6]dec-4-en-3-one by IUPAC nomenclature, provide its molecular formula.
user
C21H26O3
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