Summation of series to infinity

Summation of series to infinity

I was doing some math problems when I got stuck at summing the series of
the form ∑_(n=∞)^(n=1)▒〖x^(a^n ) where
x<1&#12311; and a is any positive integer since x^n>x^(a^n ),the series
converges by Comparison test.I tried everything I knew but I couldn't' t
produce the solution