Number pattern rules

In a growing pattern like 2, 5, 8, 11, each term is a fixed amount bigger than the one before — here it goes up by 3 each time. That fixed amount is the common difference. To find a later term without writing them all out, notice there is one fewer jump than the term number: the 6th term is 5 jumps of 3 added to the start. So 2 + 5 × 3 = 17. Count the GAPS, not the terms, and never forget to add the starting number.