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.
Answer: GCF of 13 and 17 is 1. 2.
Step-by-step explanation: Greatest common factor (GCF) of 13 and 17 is 1. We will now calculate the prime factors of 13 and 17, than find the greatest common factor (greatest common divisor (gcd)) of the numbers by matching the biggest common factor of 13 and 17.
Answer: 4
Step-by-step explanation: