-7,7,11,17,19,21,23,29,…以后的都是以这8个数的循环,求此数列的通项公式?

X(n)=X(n-8), X(0)=-7, X(1)=7, X(2)=11, X(3)=17, X(4)=19, X(5)=21, X(6)=23, X(7)=29