Mathematics for IGCSE & O level - Sequences (Section 3 - No. 32)
Which of the following sequences is *not* an arithmetic sequence?
1, 2, 3, 4, ...
3, 6, 9, 12, ...
2, 4, 8, 16, ...
10, 7, 4, 1, ...
Explication
An arithmetic sequence must have a common difference.