It's not entirely clear what you're after, but I think I have the idea.
You have this data:
| A | B
----------------------------------------------------
1 | 12760
2 | 15464
3 | 17162
4 | 19808
5 | 22757
6 | 25450
And you want column B to show the difference between the value in column A and the value in column A in the row above. That's really quite simple.
In B2 put the formula:
=A2-A1
Then you can autofill that down the rest of column B as far as you need.
For the first row, since there's an implied zero, just put in B1
=A1
In the end, you'll have:
| A | B
----------------------------------------------------
1 | 12760 | 12760
2 | 15464 | 2704
3 | 17162 | 1698
4 | 19808 | 2646
5 | 22757 | 2949
6 | 25450 | 2693
(If this isn't what you're after, then please edit your question to provide further clarity.)