a2=1/(1-3)=-1/2a3=1/(1+1/2)=2/3a4=1/(1-2/3)=3这列数,是3,-1/2,2/3.。。循环冲轮每贺判信组3个禅轮2011÷3=670余1a2011=a1=3
a1=3a2=1/(1-3)=-1/2a3=1/(1+1/2)=2/3a4=1/卖此(1-2/3)=3所以三碰棚个一笑配则组循环2011/3=670……1所以a2011=3