8．
如果有穷数列\(a_{1}\)，\(a_{2}\)，\(…a_{m}(m\)为正整数\()\)满足条件：\(a_{1}=a_{m}\)，\(a_{2}=a_{m-1}\)，\(…a_{m}=a_{1}\)，则称其为“对称数列”\(.\)例如数列\(1\)，\(2\)，\(5\)，\(2\)，\(1\)与数列\(8\)，\(4\)，\(2\)，\(4\)，\(8\)都是“对称数列”\(.\)已知在\(21\)项的“对称数列”\(\{c_{n}\}\)中，\(c_{11}\)，\(c_{12}\)，\(…\)，\(c_{21}\)是以\(1\)为首项，\(2\)为公差的等差数列，则\(c_{2}=(\) \()\)