emacs org-mode tblfm: cumsum in table column

|   x | \cumsum x |
|-----+-----------|
|   0 |           |
|  68 |        68 |
| 135 |       203 |
| 203 |       406 |
| 270 |       676 |
| 330 |      1006 |
| 390 |      1396 |
| 450 |      1846 |
| 495 |      2341 |
#+tblfm: @3$2..$2=$1+@-1$2