You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by 2-(6-oxopyrimidin-1-yl)-N-[3-(3-thiophen-2-yl-[1,2,4]triazolo[4,3-b]pyridazin-6-yl)phenyl]acetamide ?
user
C21H15N7O2S
assistant