intzip
Fast compression of integer sets.
...An arbitrary set of integers (i.e., a collection of unique numbers where the order does not matter) may be transformed into suitable input data by way of translation and sorting.
The main focus of the algorithm is to encode structural characteristics of a given list, such as coherent intervals and repeated distances. Therefore, the quality of compression depends on diversity rather than size. In most cases, IntZip is able to achieve much better compression results than general compression algorithms on such data sets.