Jeff - I think that it is almost the sawtooth just missing an amp/2 factor which you then subtract the above sum from. See sawtooth for details.
To see the sawtooth take shape as n increases, try the following code
close all;
figure;
% define the number of samples per second
Fs = 8192;
% create your one second time vector
t = linspace(0,1-1/8192,Fs);
% define your frequency and amplitude
f = 2;
amp = 1;
% plot dummy data
h=plot(NaN,NaN);
res = amp/2;
for k=1:n
res = res - (amp/(k*pi))*sin(2*pi*k*f*t);
set(h,'XData',t,'YData',res);
pause(0.1);
end
