What Do You Consider Rare?

50, 20, 10... One day I hope to have such a note in my collection.

There are just so many aspects to this, especially with paper money, where each note is demonstrably unique. Condition rarities, of course, exist for every series and denomination - a truism. Pop reports, especially for NBNs, also reflect rarity (such as MVC's - certainly a 4 or 5 pop note has to be rare by definition).

And of course, serial numbers, with all their permutations, present an explosion of theoretical rarities - solids, ladders and god knows what. Personally, I feel that any single-digit serial number is rare, but you could certainly argue that solids and others are equally rare by mathematical deduction.

I don't think these factors can be summed up in a simple formula unless you set the condition rarity category aside, in which case I would say that "rare" means less than 10 examples known in a given category (NBNs by bank or denomination, regular issues by type, denomination, series and prefix/suffix).

And of course, NONE of this has much to do with value!