Goldbacks with 4 of the same number in its serial number

4 of a Kind

If you rolled 5 dice in a game and 4 of them were of the same number, you would immediately recognize it and your friends would be jealous. The same is true with a Goldback note with 5 digits. It is even rarer to get 4 of the same kind with a serial number because there are 10 rather than 6 numbers.