Answer:
[tex]2^{n-1}[/tex]
Step-by-step explanation:
[tex]\text{It is a geometric series.}\\\\\text{First term,}~ a = 1\\\\\text{Common ratio,}~ r = \dfrac 21 = 2\\\\\text{Nth term,}~ a_n = a r^{n-1}\\\\~~~~~~~~~~~~~~~~~~~=1\cdot 2^{n-1}\\\\~~~~~~~~~~~~~~~~~~~=2^{n-1}[/tex]
