Use value in cell as numeric reference to a row, within a sum func

[Guest]

I would like to be able to use a value in a cell as the numeric reference to
a row in another column, to which to sum values in that column.
Eg.
If A5 = 7, sum values in cells D3 to D7.
If A5 = 13, sum values in cells D3 to D13.

 

[Dana DeLouis]

Just another option:

=SUM(OFFSET(D3,0,0,A5-2,1))