sigma_error.c running, n=100 
x 1 .. 100 
sum x^2 - (sum x)^2/n  sigma1 = 28.8661 
sum(x-mean)^2/n  sigma2 = 28.8661 
x 10 .. 1000 
sum x^2 - (sum x)^2/n  sigma1 = 288.66 
sum(x-mean)^2/n  sigma2 = 288.661 
x 100 .. 10000 
sum x^2 - (sum x)^2/n  sigma1 = 2886.61 
sum(x-mean)^2/n  sigma2 = 2886.61 
x 1000 .. 100000 
sum x^2 - (sum x)^2/n  sigma1 = 28866.1 
sum(x-mean)^2/n  sigma2 = 28866.1 
x 10000 .. 1000000 
sum x^2 - (sum x)^2/n  sigma1 = 288661 
sum(x-mean)^2/n  sigma2 = 288661 
x 10001 .. 10100 
sum x^2 - (sum x)^2/n  sigma1 = 28.9772 
sum(x-mean)^2/n  sigma2 = 28.8661