Define $p_{n,m}$ by
$p_{n,1}=p_n$ and
$p_{n,m}=p_{p_{n,m-1}}$,
where $p_n$ is the prime number function.
Conjecture:
$n^n<p_{n,n}< (n+1)^{(n+1)}$
I've only tested it for $n=1,\dots,11.$
I need help testing the conjecture for $n>11$ and to prove it. Perhaps the conjecture is a consequence of PNT?
n n^n p_{n,n} (n+1)^{n+1}
1 1 2 4
2 4 5 27
3 27 31 256
4 256 277 3125
5 3125 5381 46656
6 46656 87803 823543
7 823543 2269733 16777216
8 16777216 50728129 387420489
9 387420489 1559861749 10000000000
10 10000000000 64988430769 285311670611
11 285311670611 2428095424619 8916100448256
Calculate $p_{n,m}$ by m times iteration:
1. $p_{n,1}=p_n$
2. $p_{n,2}=p_{p_{n,1}}$
..
m. $p_{n,m}=p_{p_{n,m-1}}$
Using a lower bound $p_n>n\log n$, one can show that $\log{p_{n,m}}>\log{p_{n,m-1}}+\log\log{p_{n,m-1}}$. By computer, one can check that $\log{p_{26,26}}>89.0>\log27^{27}$.
It looks like always $\log{p_{n,n}}>\log(n+1)^{n+1}$ for $n\ge26$, but I can't prove it...