Is 3 a letter in Russian?

Could you please clarify for me? I'm a bit puzzled about something. Is the number "3" considered a letter in the Russian language? I'm aware that in English, numbers and letters are distinct categories, but I'm not so familiar with the Russian alphabet and its nuances. Could you explain if "3" is categorized as a letter in Russian, or if it remains strictly a numerical symbol? Thank you for your assistance in clarifying this matter for me.