From my observation :- this is what they are doing.. total ways to arrange 9 numbers = 9!
For denominator, start from root node, visit every node and multiply the result with number of nodes present in that subtree.
Eg here for root node :- subtree has 9 nodes,
For left child of root :- subtree has 5 nodes,
For right child of root :- subtree has 3 nodes...
So on calculate for every node to obtain denominator.
You will get 9x5x3x3x1x1x1x1x1
Now Why are they doing this?