Exponential interpolation in CS5 using expressions

I need to exponentially easeOut a number over time.

I am using:
num = easeOut(thisComp.layer("earthComp1").transform.scale[0],0.0015,273,20000000,100);

and it's close but I need the values 20000000-100 to ease out exponentially across time (not just ease out).

Wish I paid more attention in math... can you help?

Orchard Film Studios, Canada