In this sequence, we can see that a_1 =1. a_2 =2. NOte that

Also, note that

If we do this term by term, we can see that if we take one term and divide it by the previous one, we will always get the number 2.
This type of sequence receives the name of a geometric sequence, where

where a is the first term, r is the common ratio (the one obtained from dividing one term by the previous one)