The first n terms and Sn = - n Λ 2 + 9N + 2 (n belongs to n *) of sequence an are known Judge whether it is arithmetic sequence or not

The first n terms and Sn = - n Λ 2 + 9N + 2 (n belongs to n *) of sequence an are known Judge whether it is arithmetic sequence or not

No, obviously, Sn = [A1 + an] * n / 2, there is no constant term 2