You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named sodium;(19S)-19-ethyl-14,18-dioxo-17-oxa-3,13-diazapentacyclo[11.8.0.02,11.04,9.015,20]henicosa-1(21),2,4,6,8,10,15(20)-heptaen-19-olate by IUPAC nomenclature, provide its molecular formula.
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C20H15N2NaO4
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