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 3-[5-bromo-2-[[5-bromo-3-(3-sulfopropyl)-1,3-benzothiazol-3-ium-2-yl]methylidene]-1,3-benzothiazol-3-yl]propane-1-sulfonic acid is given. What is its corresponding molecular formula?
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C21H21Br2N2O6S4+
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