While researching on the elementary proof of Bertrand's Postulate I came to know about a theorem of Rosser's which states that $p_n$ $>$ $n$ $\text{ln}$ $n$. I have seen Rosser's original proof and I am interested in shorter proof of the result. It will be best if it could be proved using elementary methods. Any suggestion will be appreciated.


1 Answer 1


There is an elementary proof by Chebyshev, which shows that $p_n>\alpha n\log(n)$ for a constant $a<1$ close to $1$. However, for $\alpha=1$ one needs more, i.e., one needs the techniques of Rosser and Schoenfeld, using zero-free regions for the Riemann zeta function. I think there is no easier proof than the one of Rosser. Piere Dusart has sharpened the estimates on the $n$-th prime. This is perhaps easier to read. References can be found in the answers here.

  • $\begingroup$ Is there any way to arrive at the result without using Prime Number Theorem? $\endgroup$
    – user170039
    Oct 26, 2014 at 17:23

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