A triviality about numbers that look like abbc

from blog The Universe of Disco, | ↗ original
Looking at license plates the other day I noticed that if you have a four-digit number with digits , and , then will always be a multiple of . For example, and . Mathematically this is uninteresting. The proof is completely trivial. (Such a number is simply , and .) But I thought that if someone had pointed this out to me when I was eight...