Denote the sequence by 
with 
.
Recursively:
The first number is
, and each successive number is twice the previous one. So 
, 
, 
, ... .
In other words,
and so in general,
Explicitly:
We can arrive at this formula by, in a way, working backwards. If, that means 
, and so 
, and so on. We would end up with
(You'll notice a pattern here: the exponent of the 2 and the index of the earlier term in the sequence add up to
. For example, 
.)
or simply
Then the 15th term is obtained immediately by evaluating this rule at
. We get
Recursively:
The first number is
In other words,
and so in general,
Explicitly:
We can arrive at this formula by, in a way, working backwards. If
(You'll notice a pattern here: the exponent of the 2 and the index of the earlier term in the sequence add up to
or simply
Then the 15th term is obtained immediately by evaluating this rule at