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What is the molecular formula of the compound with this IUPAC name (1S,2S,3R,7R,16S,17R,18R)-10-methoxy-15-oxo-6,21-dioxa-14-azahexacyclo[16.2.1.01,16.02,14.03,7.08,13]henicosa-8(13),9,11,19-tetraene-17-carboxylic acid ?
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C20H19NO6
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