Learn Russian: Мне нравится число двенадцать.

All Russian numbers from 11 to 19 end in -надцать. This ending historically comes from the phrase на десять, meaning 'on ten.' So, двенадцать literally translates to 'two on ten.' Notice that it ends with a soft sign (ь), which makes the final 't' sound soft.

Does the number двенадцать change its ending in this sentence?

No. Here, you are using a 'bare numeral'—just stating the name of the number itself rather than using it to count objects (like 'twelve apples'). Because the phrase число двенадцать is the subject of the sentence (the thing that is pleasing to you), the number stays in its basic dictionary form.

Why is the word число used here instead of номер?

In Russian, число is used for mathematical numbers, quantities, or dates. The word номер is used for an identifying number in a sequence, like a phone number, a hotel room, or a bus route. Since you are talking about twelve as a concept, число is the correct choice.

Why does the sentence start with Мне нравится instead of Я?

To express that you like something in Russian, you commonly use the verb нравится (is pleasing). This structure requires the person experiencing the feeling to be in the dative case ('to me'). Мне is the dative form of я (I). Literally, the sentence means 'The number twelve is pleasing to me.'