sigma_error.java running, n=100
x 1 .. 100 
sum x^2 - (sum x)^2/n  sigma1 = 28.86607
sum(x-mean)2/n  sigma2 =28.86607
x 10 .. 1000 
sum x^2 - (sum x)^2/n  sigma1 =288.66034
sum(x-mean)2/n  sigma2 =288.6607
x 100 .. 10000 
sum x^2 - (sum x)^2/n  sigma1 =2886.608
sum(x-mean)2/n  sigma2 =2886.607
x 1000 .. 100000 
sum x^2 - (sum x)^2/n  sigma1 =28866.074
sum(x-mean)2/n  sigma2 =28866.072
x 10000 .. 1000000 
sum x^2 - (sum x)^2/n  sigma1 =288661.44
sum(x-mean)2/n  sigma2 =288660.72
x 10001 .. 10100 
sum x^2 - (sum x)^2/n  sigma1 =28.977232
sum(x-mean)2/n  sigma2 =28.86607