I came across this symbol (the one looks like 3) when I read a book this afternoon. I never saw such a symbol before. Is it a Greek letter? What is its LaTeX code?
this is almost certainly a fraktur Z --
while the letter does look quite like the cyrillic Ze, in western math there is a very long history of using the fraktur alphabet, but the only "common" cyrillic letter i know of that has made its way into western math is the Sha (first letter of the name shafarevich, and also used for the shuffle product).