Given an integer n, it generates a tree by the following operation.
Initially, there is a node weights n.
If n is not a prime number, the nodes gets a left son and a right son, the left son weights x, where x is a factor of n and x is larger than 1 and smaller than n chosen randomly, and the right son weights n/x. We call this step split.
For each leaf of tree, we do the split operation, until all of the leaves weight a prime number.
For example, suppose n to be 12, and the picture below shows a tree generated.
Now we want to know the expectated height of the tree.