I recently found some really great bounds to a function.
g(n) = n2ⁿ
f(n) = n g's on n
e.g.
f(1) = g(1)
f(2) = g(g(2))
f(3) = g(g(g(3)))
I found the bounds of
n*(x^x^...^x) ≤ f(n) ≤ y^y^...^y^n
where there are exactly n powers of x and y, and x=2ⁿ, y=2*(n^(1/n))