Suppose $f:\mathbb{Z}\_{\geq 0}\to\mathbb{Z}\_{\geq 0}$ is an arithmetic function that grows slower than the identity map. Has it already been conjectured that, under this general hypotheses, $\pi(n+f(n))-\pi(n-f(n))\sim \dfrac{2f(n)}{\log n}$? Or are there any known counterexamples?  

Thanks in advance.



Has this strengthening of the PNT already been conjectured?
[This paper](http://www.math.boun.edu.tr/instructors/yildirim/paper/paper9.pdf) by Yildirim gives a good survey on this. Clearly, the question is equivalent to determining functions $\Phi$ such that $\pi(x+\Phi(x))-\pi(x)\sim \frac{\Phi(x)}{\log x}$. Quoting the paper, this was proved by Heath-Brown for $\Phi(x)=x^{\frac{7}{12}-\varepsilon(x)},\varepsilon(x)\to 0$, and assuming the Riemann hypothesis, we can take $\Phi(x)=x^{\frac{1}{2}+\varepsilon}$. However, $\Phi$ cannot increase too slowly, as $\Phi(x)=(\log x)^{\lambda}$ does not work for any $\lambda$ due to a result of Maier.


