an=0.6+0.06+……+6*10^(-n)=0.6*(1-0.1^n)/(1-0.1)=2/3-2/3*0.1^n
所以Sn=2/3*n-2/3*(0.1+0.01+……+0.1^n)
=2/3*n-2/3*0.1(1-0.1^n)/(1-0.1)
所以S10=179/27+2/27*0.1^10