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Name the molecular formula for the molecule established as 6-ethyl-5-methyl-2-[(5-methyl-1,2,4-oxadiazol-3-yl)methylsulfanyl]-3-[(4-methylphenyl)methyl]thieno[2,3-d]pyrimidin-4-one using the IUPAC nomenclature.
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C21H22N4O2S2
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