Numbers In Step

An arithmetic sequence is a list of numbers where you add the same amount to get from one to the next. Take 4, 9, 14, 19, 24. Each step adds 5. That fixed gap is called the common difference, written d.

That one rule does a lot of work. It means the sequence never speeds up or slows down — it marches in even strides forever. Stair steps, the seats in a stadium row, a paycheck that rises by the same raise each year: all of them count in arithmetic step. Once you spot the constant gap, you can predict any number in the list without writing the whole thing out.