Here is a simple way through a formula
Lets say that you have the values in column A
=IF(A2<>"";"";IFERROR(B1+1;1))
The logic is to check if you have any value in the same row. If there is something then leave blank
If the cell if empty then return what you had in the column with your numbering bigger by one.
The iferror is for the first row where you want to start the numbering. As you get an error by adding 1 to a text value, then just return 1.
If you want to have the original value and the subsequent numbers in the same column, then the formula would be something like
=IF(A2<>"";A2;IFERROR(B1+1;1))
| value in column A | 1st solution | 2nd solution |
| A | | A |
| | 1 | 1 |
| | 2 | 2 |
| B | | B |
| C | | C |
| | 1 | 1 |
