题目

More than loo genes are related with increased risk of developing schizophrenia（精神分裂症）,bipolar disorder （躁郁症）and alcoholism（酗酒）,confirms a large study published in the recent issue of the British scientific journal Nature.The world's largest study into the genetic basis of mental illnesses was led by researchers from British universities,including University College London (UCL),Cardiff University and King's College London (KCL).Researchers believe that they are now much closer than before to understanding the complex biological causes, which make some people be在等差数列{an}中，a1+a2+a3=0，a4+a5+a6=18，则数列{an}的通项公式为    ．