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system
Name the molecular formula for the molecule established as (3aS,10bS)-2-phenyl-3a-(phosphanylmethyl)-5-prop-2-enyl-6,10b-dihydro-[1,3]oxazolo[4,5-d][2]benzazepin-4-one using the IUPAC nomenclature.
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C21H21N2O2P
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