Jim,
The number on my old belt was 221-3775.
However, I had a belt that I had bought a few years ago for my 05 also with a C13 and its number is
211-5022 CAT F5211F2.
As I needed to change the belt I used the new belt. It appeared to me be the same length, same width, I.e same number of ribs, so I used it. No issues yet.
I do believe that when I was ordering a replacement spare the first number comes up on the CAT system.
Jeff