Are both parts of a record's Unique ID unique?

I’m trying to generate a Unique Code but it occurs to me that I could just use the UniqueId field.

I notice that all these autogenerated numbers are in the same format which is 13 numbers, X, 18 numbers.

Are both sides of the X unique? I ask because I think it would suffice for me just to use the first side and even truncated a little because otherwise the number is a little unweildy for humans to recite. I could be wrong as the sample I’m looking at probably isn’t big enough to draw a reliable conclusion.

Many thanks in advance.