You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 5-oxo-N-[3-(2-phenylethynyl)phenyl]-[1,3]thiazolo[3,2-a]pyrimidine-6-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C21H13N3O2S
assistant