Other topics to cover on the same subject: Monte Carlo methods, pseudorandom numbers, and their generators tests for randomness
Randomness is an important and useful concept in Mathematics which is, unfortunately, very difficult to define.

If a sequence of numbers is chosen from a set, the sequence is said to be random if each number, at every choice, is equally likely to be selected.

In this case, the process determines whether the numbers are random.

However random number generators in computers and calculators fail this definition absolutely, as the process chosen to generate the sequence of numbers is deterministic. If you knew the method that has been chosen by the designers of the device, you can predict the numbers exactly.