It is a standard exercise in elementary combinatorics to calculate the number of ways of rolling any given value with 2 fair 6-sided dice (by taking the sum of the two rolls). The below table enumerates the number of such ways of rolling a given value $n$:

A somewhat (un?)natural question is to ask whether or not there are any other ways of re-labeling the faces of the dice with positive integers that generate these sums with the same frequencies. The surprising answer to this question is that there does indeed exist such a re-labeling, via the labeling

and a pair of dice with this labeling are called a set of crazy dice. It is straight-forward to verify that the various possible sums occur with the same frequencies as given by the above table.