An arithmetic sequence is a list of numbers where each term increases or decreases by the same amount (called the common difference).2, 4, 6, 8, 10 → (common difference: +2)10, 7, 4, 1, -2 → (common difference: -3)5, 10, 15, 20, 25 → (common difference: +5)100, 90, 80, 70, 60 → (common difference: -10)1, 3, 5, 7, 9 → (common difference: +2)