Curve Number equation in ArcGIS Raster Calculator?

I have a floating point raster of Curve Numbers (70-91) and I’m attempting to use the curve number equation to create a weight raster for flow accumulation, to determine runoff for a single rainfall event. I’m familiar with this curve number equation:

Q = (P – 0.2S)2 / (P + 0.2S)

where

Q = total runoff
P = preciptation (1 inch in this case)
0.2S = initial abstractions
0.8 = potential maximum retention after runoff begins

The 2 outside the first bracket means to the power of 2. Firstly, I am unsure how to calculate to the power of 2 in raster calculator. Also, would precipiation be an input raster or just a value (1 for example)?