$\log \left(k.k/2.k/4\ldots 1\right)= \log \left(k^n \left(1.1/2.1/2^2.1/2^3\ldots 1\right)\right)=\log\left(k^n \frac{1}{2^0.2^1.2^2 \ldots 2^n}\right)$
$=\log\left(k^n\left(\frac{1}{2^{0+1+2+\ldots +n}}\right)\right)$
$=\log\left(k^n\frac{1}{2^{n(n+1)/2)}})\right)$
$=n\log k-\frac{n(n+1)}{2}\log 2$