The data appears to be an exponential function.
The function of this graph is y=2.8^(x-2.8)
Domain: x is greater than or equal to zero
Range: y is greater than or equal to zero
Domain: x is greater than or equal to zero
Range: y is greater than or equal to zero
The negatives don't matter because you cant have negative downloads. if you try to extend the data points, it wont make a difference because the range and domain will be the same.