Answer
$a_{n}=\frac{1}{2n-1}$
Work Step by Step
{$\frac{1}{1},\frac{1}{3},\frac{1}{5},\frac{1}{7},\frac{1}{9}, ...$}
The numerators: always 1
The denomitators: $1,~3,~5,~7,~9,~... $
That is: $2 - 1,~4 -1,~6-1,~8-1,~10-1,~...,~2n-1,~...$
Thus:
$a_{n}=\frac{1}{2n-1}$
