A formula is recursive if it expresses the term in terms of the previous one(s)
In this case, every term is 7 more than the previous one, so the formula for will only involve
:
In fact, this formula is simply saying: for every index , the term with that index is 7 more than the term before.
Also, we have to specify the starting point (otherwise we would go backwards indefinitely), so the complete recursive formula is
which means: start with 2 and generate every other term by adding 7 to the previous one.