题目

阅读理解 Last week, 169 Junior 1 students at No. 35 Middle School of Shenyang took their first no-teacher exam. After the teacher handed out the exam paper, he left the room and never came back. A student collected in the papers when the exam ended. That test was not only a test of knowledge, but also a test of moral (道德). We wanted to show students how important honesty (诚实) is, said the school's headmaster. The school says no cheating (作弊)happened in the test. Next year, it wants 80% of its exams to be without teachers. But students have different ideas. I was happy {an}为等比数列，a2＝6，a5＝162，则{an}的通项公式an＝________．