What's a random number block?
There are certain sorts of probabilistic calculations, known as Monte-Carlo simulations, that require large numbers of random numbers. These used to be printed in data books, the most well known one being produced by the RAND corporation back in the 1940's (I think), called A Million Random Digits. The digits were generally printed in blocks of 5 or so separated by spaces. Perhaps these are what you are referring to. Nowadays, random digits (or pseudo-random digits) tend to be generated by clever algorithms in the computer codes that make use of them.