You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 2-chloro-N-cyclobutyl-6-methyl-7-(4-methylphenyl)sulfonylpyrrolo[2,3-d]pyrimidin-4-amine by IUPAC nomenclature, provide its molecular formula.
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C18H19ClN4O2S
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