A type of intelligence test item or subtest in which the respondent has to find a number to complete a sequence of numbers. A typical example is: What is the missing number in the following sequence? 0, 2, 8, 18, …. Although there is always an infinity of mathematically justifiable answers, the ‘correct’ answer in this case is 32, because the steps between adjacent numbers are 2, 6, 10, which are alternate even numbers, so the step between 18 and the missing step should be 14, making the missing number 32. See also completion test. Also called a number sequence, a number series, a sequence completion, or a series completion.