Your analysis is correct.
The last line: return the current value of n plus anything that would be the result of the same calculation for n-1.
But... this function does not work. As soon as you enter the function, it doubles the value of n (as you correctly said before). The recursion terminates when (you do not call the recursive function anymore) n reaches 1. What number doubled equals 1? 0.5
But the code you shared is called with n=12 and it will keep growing, and will never reach 0.5, so this is an infinite recursion and the runtime will terminate the program.
By the way, the code you shared in the question is different from the code you linked. The one you linked is also an infinite recursion, but for that, you'll need an integral that is no larger than 1 (so it could be 1, 0, -1, -2, etc) and then the recursion will naturally terminate and a result is produced.