Trace the pattern:

$x1 = 2$

$x2 = 2*x1 -1 = 2*2 -1 = 3 = 2^1 + 1$

$x3 = 2*x2 -1 = 2*3 -1 = 5 = 2^2 + 1$

$x4 = 2*x3 -1 = 2*5 -1 = 9 = 2^3 + 1$

$x5 = 2*x4 -1 = 2*9 - 1 = 17 = 2^4 + 1$

Hence, answer is $2^{n-1} +1$

$x1 = 2$

$x2 = 2*x1 -1 = 2*2 -1 = 3 = 2^1 + 1$

$x3 = 2*x2 -1 = 2*3 -1 = 5 = 2^2 + 1$

$x4 = 2*x3 -1 = 2*5 -1 = 9 = 2^3 + 1$

$x5 = 2*x4 -1 = 2*9 - 1 = 17 = 2^4 + 1$

Hence, answer is $2^{n-1} +1$