Thank you for your response. Didn't I tell you I was rusty? With all this concern over NFPA 70E - Arc Fault Protection I needed to quickly calculate the incident energy of an arc in open air. So rather than an exponential function I had intended to seek help on writing an excel equation for an expression that had a number raised to a power. Never-the-less, I did come up with an expression as shown below. It represents the equation found in NFPA 70E, B-5.1 for an Arc in Open Air with result in cal/cm-sqd.
=5271*(POWER(C2,-1.9593))*C3*((0.0016*C4*C4)-(0.0076*C4)+0.8938)
Thank you, again.