You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Translate the chemical IUPAC name (4R,4aS,8aR)-4-(4-nitrophenyl)-2-phenyl-4,4a,5,6,7,8a-hexahydropyrano[2,3-b]pyran-3-carbonitrile into its molecular formula.
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C21H18N2O4
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