How do I handle matrix calculations too big for Excel

I have a simple problem (with a complicated solution, I expect)

The formula for calculating the GINI coefficient can be found at the linked URL

http://www.adb.org/Statistics/Poverty/G.asp#gini

The only required input is a set of data points yi, the population (=count(yi)) and the average income (=average(yi).

My problem is that MY single column has 5000 data points (yi, i=1...5000), and I now need to do the nested sums without the aid of the simple 5000x5000 matrix which would have solved my problem (as you know Excel only has 256 columns)

Any suggestions??