Objectively, based on utility, they have a value of zero.
Subjectively, based on how someone
feels about them, that's down to the individual. But still zero for me, personally.
If what you're inscribing doesn't represent something tangible, it's probably worthless in my view.
Also a bitmap with the number 999999 will have a higher value then a common number like 718291, so yes I think they can be valued by the rarity of their numbers.
What the hell kind of math did they teach you in school? Mathematically speaking, if you list every number in order, without repeats, then every number is equally common. They will all appear once and once only. '718291' won't appear more often than '999999'. It's all just a lame attempt to sell junk to idiots.