sequences and series - Find the value of $n$.

Write the value of $n$ if the sum of n terms of the series $1+3+5+7...n =n^2$.

I'm not getting the right value if I proceed with the general formula for finding sum of n terms of a arithmetic series. The general summation formula for arithmetic series is $\frac{n(2a+(n-1)d)}{2}$, where $a$ is the first term, $d$ is the common difference and $n$ is the number of terms.