You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named N'-(2-methyl-5-nitrophenyl)-N-[[1-(pyridin-4-ylmethyl)piperidin-4-yl]methyl]oxamide by IUPAC nomenclature, provide its molecular formula.
user
C21H25N5O4
assistant