Defining a natural variable n in TI-Nspire CAS

I'm wondering if it's possible to define a natural variable n in TI-Nspire CAS. For example I'd like to write:

You can't define your own natural variables. However, Nspire has the following special variables you can use:

• @n0...@n255: Restricted to natural numbers
• @c0...@c255: Restricted to real numbers

You can replace the original variables with them by hand or for convience just put |x=@n0 and y=@n1 at the end of line.

Example: You are calculating fourier coefficients and know that variable k will only get real numbers from Σ operation. Replacing k with @n1 will simpilfy the function. Picture

(Calculator needs to be in RAD mode if you want to try)