You can create random numbers using a function called RANDOM(). Even though the function is not shown within the functions in calculative field.
RANDOM() returns a decimal number from [0 - 1]. This function does not take any arguments/parameters.
To get a integer big number ,you can use one or more random function together and multiply with 10^4 or higher power.
Create random numbers using calculated field. ( I used 10^5 as multiplication number, you can choose even any number. To avoid duplicates i used 2 random() functions. )
After adding the field to the table .
Hope this helps you.