This is a Geometric Sequence. The common ratio (r) is 2. That is, each term is 2 times the previous term. The first term is 7.
As a recursive definition, we would write it as:
a1 = 7
an = 2*an-1 [for n>1]
Using a recursive definition, you must find all of the previous terms before you could find the nth term.
As an explicit definition, we would write it as:
an = 7*2n-1 [for n>0]
Using an explicit definition, you may find a term directly. For example, the 5th term in this sequence,
a5 = 7*25-1 = 7*24 = 7*16 = 112