@1$2 = @1$1 - @1$1
@2$2 = @2$1 - @1$1
@3$2 = @3$1 - @2$1
...

| x | delta |
|---+-------|
| 2 |     0 |
| 3 |     1 |
| 5 |     2 |
| 1 |    -4 |
| 7 |     6 |