Although you haven't said so explicitly, it seems as though you are talking about Fibonacci sequences, since the usual notation for that in Mathematics/Computer Science classes is F(n), and the routines are recursive. The Fibonacci sequence is defined as:

`F(n)=F(n-1)+F(n-2)` , where `F(2)=1` and `F(1)=1` .

which means that

`F(4)=F(3)+F(2)`

And we can see that the recursive calls continue as

`F(3)=F(2)+F(1)`

**This means that the call of `F(1)=1` is called only once.**