if we are interested to seek for the numbers of primes between $1-100$ and $100-1000$ or 1000…, why we don't asked if there is a always a prime between $n$ and $2n$ mayeb this interesting question help us to predict the numbers of primes between $1-100$,or $100-1000 $ or $1000-..$?
note: $n$ is natural number $ > 1$
I would be interest for any replies or comments .Thank you
Best Answer
$$\begin{array}{l}\text{Chebyshev said it,}\cr \text{And I say it again,}\cr \text{There is always a prime}\cr \text{Between n and 2n.}\end{array}$$
http://en.wikipedia.org/wiki/Bertrand%27s_postulate