You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (4-pyridin-2-ylpiperazin-1-yl)-(3-thiophen-3-yl-5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-6-yl)methanone by IUPAC nomenclature, provide its molecular formula.
user
C21H23N5OS
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