Explain it to me like I'm mediaeval peasant who knows not what are numbers or a zero: what is a "special" ID.

I'm trying to buy a dragon and seller is demanding more because the ID is, supposedly, special but it's not a palindrome, neither sequential nor prime nor has fun numbers like 69 or 420 nor is a birthday nor anything else I can imagine. I was willing to pay a lot for it until the seller seems to have started to invent reasons to make it cost more, dude, just say you want more treasure...