ones

I agree it is extremely difficult on Euros. If my calculations are correct, then only German Euro notes can have the number X11111111111. And if I remember correctly, Ireland and one other country can have 22222222222.

I collect banknotes with exactly all 1's in their serial numbers (11111111), and I managed to "find" over a hundred of these from around 50 different countries/issuing authorities. It is actually not extremely difficult to purchase banknotes with this type of numbers from many countries. If the demand of collectors from a country is high enough, then these notes will almost always be kept by the bank employees or even by the issuing department (for auction sale). By the way, if anyone has any 1111111 notes for sale I would be glad to be informed.