Numbers
 1
 2
 5
10

18        Total

|  A  |  B  |
-+-----+-----+
1|  1  |     |
2|  2  |     |
3|  3  |     |
4|  4  |     |
5|  5  |     |
6|     |     |
7|  15 |Total|

|  A  |  B  |
--+-----+-----+
 1|  1  |     |
 2|     |     |
 3|     |     |
 4|     |     |
 5|  2  |     |
 6|  3  |     |
 7|  4  |     |
 8|  5  |     |
 9|     |     |
10|  15 |Total|

=SUM(INDIRECT(ADDRESS(1,COLUMN())&":"&ADDRESS(ROW()-1,COLUMN())))