I learned about apocopation in Spanish, but the online sources I have seen only say that uno is shortened to un when it precedes a singular masculine noun, but días is plural, so why is it still "treinta y un días," "cincuenta y un días," etc.? Am I missing something?
I saw this related question (Using "Uno", "Un", and "Una" and a generalization of any number with a units digit of one), but I'm still confused because I thought we'd use unos instead of un before plural masculine nouns.
I'd greatly appreciate any help, thank you!