Copy a Cell and add a Suffix

In my table for work I have a column with duty number shown in Column A in the image.

In the blank cells of Column A I want them to be filled with whatever the cell above contains but with the suffix 'A' so column A will read:

1051

1051A

1052

1052A........

I hav done this before but I cannot think how. Any guidance is greatly appreciated.

Thanks.