题目

 Children in England are not allowed to work until they are 13 years old. They need to have a work permit(许可证) to start working.The jobs teenagers can do:Delivering newspapers: Many teenagers get up early to deliver newspapers to houses in their local area before going to school. They are known as paper boys or paper girls.Babysitting: Looking after young children in their houses when their parents go out for the evening is a popular job for teenagers, as they get paid for watching children and television at the same time!Helping the milkman: From the age of 14, some teenagers can help 已知函数，数列{an}满足a1=1，an+1=f（an）（n∈N+）．（1）求数列{an}的通项公式an；（2）若数列{bn}满足，求Sn．