How do you think recursively? Any tips?

Think of fractals

Look at the 2nd grader learning f(x) for the first time. He usually starts by feeding 1 into it, seeing what results, increments by 1, and repeats until he hits his mark.

Assuming he’s going the right direction and it’s a whole number, that is...

Just think about what you are thinking.

First you must define the ending scenario, then you should figure what should the function do in "one iteration" bedfore it calls itself with different arguments.

the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
the ending scenario is very important
StackOverflowException

you don't