An=10×10^(n-1)=10^n
lgAn=lg10^n=n
{lgAn}是等差数列
Bn=(lgA1+lgA2+……+lgAn)/n
=(1+2+……+n)/n
=[(1+n)n/2]/n
=(n+1)/2
B(n+1)-Bn=(n+2)/2-(n+1)/2=1/2
{Bn}是等差数列