The first billion of digits of Pi might look pretty random, but there might be a short program which genrates them - which can be considered a compressed form.

The first billion of digits of Pi might look pretty random, but there might be a short program which genrates them - which can be considered a compressed form. In general, it is impossible to decide how good a given string might be compressed. https://en.wikipedia.org/wiki/Kolmogorov_complexity https://en.wikipedia.org/wiki/Kolmogorov_complexity