Equal Percentage characteristic can be identified by equal increments of X axis that yield equal percentage increments of the y-axis.

Whereas, in a linear characteristic, equal increments of x-axis yield equal increments in the y-axis.

Linear curve is simple as equation is just y=x.

I need help for the equation for equal percentage curve.
Either equation or how to generate it in excel will be gr8.

I have posted this picture of both linear(1) and equal percentage curve(2)  which will tell you what I am asking.
Thanks in advance