$T(a)=0 \hspace{0.2cm} if \hspace{0.2cm} a=1$
$T(a)=2T(a/2) + ak \hspace{0.2cm} if \hspace{0.2cm} a=2^{p}, p>0$
where $a=\frac{n}{k}$
Answer: $\Theta (n \log (\frac{n}{k}))$, This is while (n/k) is power of 2.
How can I solve it using master theorem?