Yesterday, I read on a website that this kind of thing is referred to as a bookend note. Here is the definition on the website:
A bookend note has a serial number having the same sequence of digits at both ends. An example is serial number 63195631. "631" is the sequence of digits appearing at both the beginning and end of the serial number.
Well, I'm not sure if there is no one collecting this kind of thing, but I'll bet there aren't many collecting bookend notes, right ?