Mathcad: how to obtain discrete differentials?

I am still using Mathcad 11, and only sometimes Mathcad 15 (hate Framenet in XP).

I do not konw how to obtain discrete differentials. The following example may explain my problem:

1. Let's start with an equation like this: y(x)=x^2 with x as a range variable: x:=0,1,..3.
2. One obtains y(x)=0, 1, 4, 9 (as a range column)
3. the derivative of y(x) (i.e. 2x) gives: DER1:= d y(x)/x = 0, 2, 4, 6, (as column range)
4. but the change of x is discrete: so the complete differential is: 2x+Delta_x.
5. Given that my Delta_x from the x range is 1, one is tempted to write DER2:=DER1+1 giving: DER2a=1, 3, 5, 7
6. Yet this is not fully correct since Delta_x is a variation, and any variation is between two values (the previous and the next). Hence it should probably be DER2b= 0, 1, 3,5,7. But I do not know how to obtain simply DER2b, with a formula like (5).

In any case, how do I obtain, starting with the initial value y(x)=0, all the range values of y(x) shown in step (2) [i.e. 0,1,4,9] using DER2a or b?

Thank you for any suggestion,

AQ