1．
定义：\(a\)是不为\(1\)的有理数，我们把\(\dfrac{1}{1-a}\)称为\(a\)的差倒数，如：\(2\)的差倒数是\(\dfrac{1}{1-2}=-1\)，\(-1\)的差倒数是\(\dfrac{1}{1-(-1)}=\dfrac{1}{2}.\)已知\({{a}_{1}}=-\dfrac{1}{3}\)，\(a_{2}\)是\(a_{1}\)的差倒数，\(a_{3}\)是\(a_{2}\)的差倒数，\(a_{4}\)是\(a_{3}\)的差倒数，\(……\)，依此类推，则\(a_{2018}=\)________．