I'm trying to plot a standard deviation function using WolframAlpha's function plotter and my function looks like this:
$SD(Y) = \sqrt{\sum_{i=2}^{k}\frac{k(i-1)}{ (k-(i-1))^2 }}$ where k goes from 1 to 50.
And I've written my function like this in the plot
plot sum( (k(i-1)) / ((k-(i-1))^2) ) from i=2 to k from k=1 to 50
But I can't seem to put a square root over the whole sum without an error. How can I write my standard deviation function and get the graph?