题干
设数列{an}，{bn}，{cn}满足a1=a，b1=1，c1=3，对于任意n∈N*，有bn+1=
，cn+1=
．
| a |
| n |
| + |
| c |
| n |
| 2 |
| a |
| n |
| + |
| b |
| n |
| 2 |
