Math's Digital learning object.

This term I have been learning to use a rule to make a number sequence as in given a rule written in words, a number sequence can be created. Remember that the numbers of  sequence can be called terms. I found this task a little bit challenging but it was something new to learn. I think I need to work on learning more about making a number sequence as in giving a rule written in words. I would like to know more about why you have to use a rule to make a number sequence.