The formula for n th term of a geometric sequence is #ar^(n-1)# where a is the first term and r is the common ratio. In the given sequence first term is 1 and the common ratio is 2. Hence nth term would be #2^(n-1)#

Note that #r=("a term")/("previous term")=2/1=4/2=8/4=16/8 = 2#