(一):1,1,2,3,2,1,1,2,3,2,1,1,2,3,2,...
(二):2,3,2,1,1,2,3,2,1,1,2,3,2,1,1,...
(三):3,2,1,1,2,3,2,1,1,2,3,2,1,1,2,...
a3=a2+1a1
a4=a3+1a2=a2+1a1+1a2=a1+a2+1a1a2
a5=a4+1a3=a1+a2+1a1a2+1a2+1a1=(a1+1)(a2+1)a1a2a2+1a1=a1+1a2
a6=a5+1a4=a1+1a2+1a1+a2+1a1a2=a1
a7=a6+1a5=a1+1a1+1a2=a2
得知數列
{an}是前5項循環的數列。