Assuming the recursive function f(x)=2x , x eof N we can see that all results are even.

Let's define that the start value of the recursion has to be odd.

f.e. we get this sequence starting with the number 3:
[3,6,12,24,...]

Here is my question: Given an even number can we find the odd start number without having to divide it by 2 until we got there?

If no, can we somehow construct an odd numbers where this is possible? It don't have to be all odd numbers.