You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named [4-(2-nitrophenyl)sulfonylpiperazin-1-yl]-(4,5,6,7-tetrahydropyrazolo[1,5-a]pyridin-2-yl)methanone is given. What is its corresponding molecular formula?
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C18H21N5O5S
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