Numbers are orderly and ranked. Two follows one, three follows two, etc.
Zero is certainly an interesting number. One is interesting because it's the identity for multiplication and other things.
If there exists an uninteresting number out there, then we could collect them all into an orderly set. That set would also be ranked. The set of uninteresting numbers would thus have a least value member. Being the least value member in the set of uninteresting numbers would make that number interesting. Therefore that number could not be in the set. Of course, its exclusion would "promote" the next least value number to being the least value in that set, making IT now interesting.
The set of all uninteresting numbers is therefore empty. If there exists an interesting number, and all numbers are ranked, and the set of uninteresting numbers is empty, all numbers are interesting.