Auto Populating a cell based on values from another cell

Hi,
1st.
Got Column A which contains part numbers (only numbers). (starting from A3)
Got Column G which also contains part numbers (only numbers) (starting from G3)

2nd.
There are times where Column A can have more or less part numbers than Column G and VS.

3rd
I like a formula that can auto generate a numerical fill-in List in Column F depending on how ever many part numbers are found in either Column A and or Column G

4th
I like this auto fill-in of numerical numbers starting from 1 to be based on which ever Column A or G has the longest list of part numbers.

Example

A3 F3 G3
75895 1 6575
3562 2 9867
46598 3 1444
85687 4
...........................................

as you see all I need is for column F to be auto populated by a numerical list starting from 1 and to continue depending on how long eighther Colum A or G are.

Thank you