Which of the following is NOT an arithmetic sequence?
2,4,6,8,…2, 4, 6, 8, \dots2,4,6,8,…
5,2,−1,−4,…5, 2, -1, -4, \dots5,2,−1,−4,…
1,2,4,8,…1, 2, 4, 8, \dots1,2,4,8,…
π,π,π,π,…\pi, \pi, \pi, \pi, \dotsπ,π,π,π,…