# A bound for a certain set of prime numbers.

Let $p_n$ denote the $n^\text{th}$ prime. Find a lower bound for $\left|S\right|$ where

$$S = \left\{ q \in \mathbb{N} \mid q \text{ is prime and } p_n - n \leq q \leq p_n + n \right\}.$$

Any good bounds known? See this graph: http://oeis.org/A097935/graph

[Edit 1] Let

$$a = n\left(\ln(n) + \frac{13}{500}\right), \ \ b = n\left(\ln(n) - \frac{987}{500}\right)$$ and $$r = \frac{a}{\ln(a)-1} - \frac{b}{\ln(b)-23/20} - 2.$$

Conjecture 1: For $n \ge 12$ $$\lfloor r \rfloor \le |S|.$$

[Edit 2] It seems that we can push things a little further. Let

$$s = \frac{a}{\ln(a)-1} - \frac{b}{\ln(b)-23/20} + \frac{a}{\ln(a)-23/20} - \frac{b}{\ln(b)-1}$$

Conjecture 2: $s/2$ and $|S|$ are asymptotical equivalent.

$$\frac{s}{2} \sim |S|$$

For the fun of it let's look at an numerical example. Let $n = 10000$. Then $|S| = 1715$ and $s/2 = 1762.31..$.