I have been given the following question in my homework:

Show that for every $n \in \mathbb{N}$ there are at least ${\log_2log_2 (n-1)}$ primes in $[1,n]$

I think it is related to euclidean and induction but I am having difficulties developing my solution.

Thanks for your help (:


Euclid's proof that there are infinitely many primes also shows that the $n$-th prime satisfies $p_n\le 2^{2^{n}}$, which also gives $\pi(n)\ge \log_2(\log_2(n-1))$ , see this MSE question.

Remark: We can easily prove a better estimate, using an elementary argument starting with $2^n\le \binom{2n}{n}<4^n$, which gives $$ \pi(n)>\frac{n}{6\log n} $$ for all $n\ge 2$ (see also this MSE question).


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