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The twin prime conjecture refers to:

$$ \liminf_{n\to \infty}\; p_{n+1} - p_{n} = 2. $$

By reasoning I arrive at the following simple formula for gaps between primes:

\begin{align} p_{n+1}-p_{n} & = \frac{p_{n+1}^{2}-p_{n}^{2}}{p_{n+1}+p_{n}}=2 \\ & \Rightarrow (p_{n}+h)^{2}-p_{n}^{2} =2(2p_{n}+h)\\ & \Rightarrow h^{2}+2p_{n}h =2h+4p_{n}\\ & \Rightarrow \frac{h^{2}-2h}{2}+p_{n}h =2p_{n}\\ & \Rightarrow p_{n} < p_{n}+h < 2p_{n} \le p_{n}h \le\frac{h^{2}-2h}{2}+p_{n}h\\ & \Rightarrow p_{n} < p_{n}+h < 2p_{n} \le \frac{h^{2}-2h}{2}+p_{n}\\ & \Rightarrow \frac{h^{2}-2h}{2} \le p_{n}-2\\ & \Rightarrow (h-\sqrt{2})^{2}\le 2p_{n}-2\\ & \Rightarrow (h-\sqrt{2})^{2}< 2p_{n} \\ & \Rightarrow h < \sqrt{2p_{n}}+\sqrt{2} \end{align}

so: $$ p_{n+1} - p_{n} < \sqrt{2p_{n}}+\sqrt{2} $$

or: $$ p_{n+1} < p_{n} + \sqrt{2p_{n}}+\sqrt{2}. $$

It's a simple conclusion, and one that is stronger and more valid than the Bertrand's postulate.

For example, we often use $[\sqrt{x},x]$ as a judgment and determination of prime number interval, and the above inference can directly give the answer.

I want to ask, is this conclusion correct?

By the way, this formula only holds if the twin prime conjecture holds.

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    $\begingroup$ Welcome to MO! Your bound $p_{n + 1} < p_n + \sqrt{2p_n} + \sqrt2$ came from $p_{n + 1} = p_n + 2$, which is much simpler, so I'm not sure what you gained. As you say, you have only proven the former inequality when $(p_n, p_{n + 1})$ are twin primes. By comparison, Bertrand's postulate is for arbirary primes. $\endgroup$
    – LSpice
    Commented Sep 27 at 10:55
  • $\begingroup$ @LSpice Thank. My main goal is to prove that there must be a prime number in the interval [p~p+$\sqrt{2p}+\sqrt{2}$ ], which is strong than there must be a prime number in the interval [p~2p]. $\endgroup$
    – Wayne
    Commented Sep 27 at 12:12
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    $\begingroup$ Re, but you have proven this only for $p$ the first of a pair of twin primes, where it is obvious. $\endgroup$
    – LSpice
    Commented Sep 27 at 12:13
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    $\begingroup$ Wayne: what @LSpice is saying is, what you have proved is that if $p_{n+1}-p_n=2$ then $p_{n+1}-p_n<\sqrt{2p_n}+\sqrt{2}$. This is not going to buy you anything at all. $\endgroup$ Commented Sep 27 at 13:10
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    $\begingroup$ Also posted to, and closed on, math.stackexchange, math.stackexchange.com/questions/4977101/… – without any notice to either site of its posting to the other, a violation of terms of both sites. $\endgroup$ Commented Sep 28 at 1:18

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Such conjectures are known in the literature. For example, Andrica's conjecture.

It is known that under the Riemann Hypothesis one has $p_{n+1} - p_n = O(\sqrt{p_n} \log p_n)$. The best unconditional result of this sort is due to Baker, Harman, and Pintz, who showed that there is always a prime in the interval $[x, x + x^{0.525})$ for $x$ sufficiently large.

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