In the following figures, smoothed is a seven day running average.
I tried fitting a cubic function to the cumulative points.
a = 984741 +/- 1.676e+05 (17.02%) b = 1.2374e+08 +/- 1.22e+06 (0.9862%) c = -8.26629e+07 +/- 2.523e+06 (3.052%) d = 2.72532e+07 +/- 1.403e+06 (5.149%)
Note - The next three graphs use a log scale.