In Merge sort Algorithm when I took input array of size 2 and I got 4 function calls as including original function call with which I call MS algorithm i.e. MS (1,2) and which in turn calls two recursive function calls to merge sort as MS (1,1) and MS (2,2) and one function call to merge procedure as Merge (1,1,2)

Likewise for input array of size 3 I got 7 function calls.

for input array of size 6 I got 16 function calls.
So, how can I analyze the total number of function calls when input array size is n?