You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-(2-ethylhexyl)-2-hydroxy-4-methyl-5-[(2-nitrophenyl)diazenyl]-6-oxopyridine-3-carbonitrile by IUPAC nomenclature, provide its molecular formula.
user
C21H25N5O4
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