A formula is recursive if it expresses the term [tex] a_n [/tex] in terms of the previous one(s) [tex] a_{n-1},\ a_{n-2},\ \ldots,\ a_1 [/tex]
In this case, every term is 7 more than the previous one, so the formula for [tex] a_n [/tex] will only involve [tex] a_{n-1} [/tex]:
[tex] a_n = a_{n-1} + 7 [/tex]
In fact, this formula is simply saying: for every index [tex] n [/tex], 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
[tex] a_n = a_{n-1} + 7,\quad a_1 = 2 [/tex]
which means: start with 2 and generate every other term by adding 7 to the previous one.
