Solution 1. We first prove inductively that the following equations hold for all i∈N:
f(1⋅4i−1)f(2⋅4i−1)f(3⋅4i−1)=2⋅4i−1,=3⋅4i−1,=4⋅4i−1=4i.
The base case follows easily from the string of inequalities
1<f(1)<f(f(1))<f(f(f(1)))=4.
The inductive step then follows from the assumed identity for f(f(f(n))).
Let A=1⋅4i−1 for some i∈N, let S be the set of integers between A and 2A inclusive, and let T be the set of integers between 2A and 3A inclusive. Since f maps the endpoints of S to the endpoints of T, the strictly increasing condition for f implies that
* f(S)⊂T, and
* S and f(S) have the same cardinality.
But S and T clearly have the same cardinality, so we must have f(S)=T, and monotonicity now implies that f(A+k)=2A+k for all 1≤k≤4i−1. In the same way, we see that f(2A+k)=3A+k for all 1≤k≤4i−1. Finally, f(3A+k)=f(f(f(A+k)))=4A+4k for all 1≤k≤4i−1. We now have a formula for f(n) for all n.
Writing 2022=1024+998=45+998, we see that
f(2022)=2⋅1024+998=3046.
Solution 2. Applying f to f(f(f(n)))=4n and then using the same equation with n replaced by f(n) we get
f(4n)=f(f(f(f(n))))=4f(n)
for all n∈N, and hence
f(4nn)=4f(4n−1n)=⋯=4nf(n).
We know f(1)=2, f(2)=3, f(3)=4 since the function is increasing with
1<f(1)<f(f(1))<f(f(f(1)))=4.
Hence f(4i)=4if(1)=2⋅4i and f(2⋅4i)=4if(2)=3⋅4i so
4i≤x=4i∑2⋅4i−1[f(x+1)−f(x)]=f(2⋅4i)−f(4i)=4i.
Thus f(x+1)−f(x)=1 for each x with 4i≤x≤2⋅4i−1. It follows that f(4i+k)=f(4i)+k=2⋅4i+k for 1≤k≤4i and hence f(2022)=2⋅1024+998=3046 as above.